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Category: SQL Server

Performance Optimization Techniques for SQL Server Queries

Transact-SQL Optimization Tips:
 Following things we can do to optimize sql queries
1)Use views and stored procedures instead of heavy-duty queries. This can reduce network traffic, because your client will send to server only stored procedure or view name (perhaps with some parameters) instead of large heavy-duty queries text. This can be used to facilitate permission management also, because you can restrict user access to table columns they should not see.

2) Try to use constraints instead of triggers, whenever possible. Constraints are much more efficient than triggers and can boost performance. So, you should use constraints instead of triggers, whenever possible.

 3)Use table variables instead of temporary tables. Table variables require less locking and logging resources than temporary tables, so table variables should be used whenever possible. The table variables are available in SQL Server 2000 only.

 4)Try to use UNION ALL statement instead of UNION, whenever possible. The UNION ALL statement is much faster than UNION, because UNION ALL statement does not look for duplicate rows, and UNION statement does look for duplicate rows, whether or not they exist.

5)Try to avoid using the DISTINCT clause, whenever possible. Because using the DISTINCT clause will result in some performance degradation, you should use this clause only when it is necessary.

6)Try to avoid using SQL Server cursors, whenever possible. SQL Server cursors can result in some performance degradation in comparison with select statements. Try to use correlated sub-query or derived tables, if you need to perform row-by-row operations.

7) Try to avoid the HAVING clause, whenever possible. The HAVING clause is used to restrict the result set returned by the GROUP BY clause. When you use GROUP BY with the HAVING clause, the GROUP BY clause divides the rows into sets of grouped rows and aggregates their values, and then the HAVING clause eliminates undesired aggregated groups. In many cases, you can write your select statement so, that it will contain only WHERE and GROUP BY clauses without HAVING clause. This can improve the performance of your query.

8) If you need to return the total table’s row count, you can use alternative way instead of SELECT COUNT (*) statement. Because SELECT COUNT (*) statement make a full table scan to return the total table’s row count, it can take very many time for the large table. There is another way to determine the total row count in a table. You can use sysindexes system table, in this case. There is ROWS column in the sysindexes table. This column contains the total row count for each table in your database. So, you can use the following select statement instead of SELECT COUNT (*): SELECT rows FROM sysindexes WHERE id = OBJECT_ID(‘table_name’) AND indid < 2 So, you can improve the speed of such queries in several times.

9)Include SET NOCOUNT ON statement into your stored procedures to stop the message indicating the number of rows affected by a T-SQL statement. This can reduce network traffic, because your client will not receive the message indicating the number of rows affected by a T-SQL statement.

10)Try to restrict the queries result set by using the WHERE clause. This can results in good performance benefits, because SQL Server will return to client only particular rows, not all rows from the table(s). This can reduce network traffic and boost the overall performance of the query.

11)Use the select statements with TOP keyword or the SET ROWCOUNT statement, if you need to return only the first n rows. This can improve performance of your queries, because the smaller result set will be returned. This can also reduce the traffic between the server and the clients.

12) Try to restrict the queries result set by returning only the particular columns from the table, not all table’s columns. This can results in good performance benefits, because SQL Server will return to client only particular columns, not all table’s columns. This can reduce network traffic and boost the overall performance of the query.

1. Indexes
 2. Avoid more number of triggers on the table
3. Unnecessary complicated joins
4. Correct use of Group by clause with the select list
5. In worst cases Denormalization

Index Optimization tips
a) Every index increases the time in takes to perform INSERTS, UPDATES and DELETES, so the number of indexes should not be very much.
b)Try to use maximum 4-5 indexes on one table, not more. If you have read-only table, then the number of indexes may be increased.
c)Keep your indexes as narrow as possible. This reduces the size of the index and reduces the number of reads required to read the index.
 d)Try to create indexes on columns that have integer values rather than character values.
 e)If you create a composite (multi-column) index, the order of the columns in the key are very important. Try to order the columns in the key as to enhance selectivity, with the most selective columns to the leftmost of the key.
f)If you want to join several tables, try to create surrogate integer keys for this purpose and create indexes on their columns.
 g)Create surrogate integer primary key (identity for example) if your table will not have many insert operations.
 h)Clustered indexes are more preferable than nonclustered, if you need to select by a range of values or you need to sort results set with GROUP BY or ORDER BY.
 i)If your application will be performing the same query over and over on the same table, consider creating a covering index on the table.
 f)You can use the SQL Server Profiler Create Trace Wizard with “Identify Scans of Large Tables” trace to determine which tables in your database may need indexes. This trace will show which tables are being scanned by queries instead of using an index.
 g)You can use sp_MSforeachtable undocumented stored procedure to rebuild all indexes in your database. Try to schedule it to execute during CPU idle time and slow production periods. sp_MSforeachtable @command1=”print ‘?’ DBCC DBREINDEX (‘?’)”

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SQL Server Database Interview Questions And Answers

Please find below post on SQL Server Database Interview Questions And Answers being asked in various organizations , we have put together a resource that we fell you would find useful.
Please leave us your feedback in form of  a comment !! You can also post any questions you have in the comment section as well.
T-SQL Queries
Tables used :
Employee
Phone
Empid,empname ,salary ,mgrid
Empid ,phnumber
Select all employees who doesn’t have phone?
SELECT empname FROM Employee WHERE empid NOT IN (SELECT DISTINCT empid FROM phone)
2. Select the employee names who is having more than one phone numbers. SELECT empname FROM employee WHERE empid IN (SELECT empid FROM phone GROUP BY empid HAVING COUNT(empid) > 1)
3. Select the details of 3 max salaried employees from employee table. SELECT TOP 3 empid, salary FROM employee ORDER BY salary DESC
4. Display all managers from the table. (manager id is same as emp id) SELECT empname FROM employee WHERE empid IN (SELECT DISTINCT mgrid FROM employee)
5. Write a Select statement to list the Employee Name, Manager Name under a particular manager?
SELECT e1.empname AS EmpName, e2.empname AS ManagerName
FROM Employee e1 INNER JOIN Employee e2
ON e1.mgrid = e2.empid ORDER BY e2.mgrid
6. 2 tables emp and phone. emp fields are – empid, name Ph fields are – empid, ph (office, mobile, home). Select all employees who doesn’t have any phones.
SELECT * FROM employee LEFT OUTER JOIN phone ON employee.empid = phone.empid WHERE (phone.office IS NULL OR phone.office = ‘ ‘)
AND (phone.mobile IS NULL OR phone.mobile = ‘ ‘)
AND (phone.home IS NULL OR phone.home = ‘ ‘)
7. Find employee who is living in more than one city. Two Tables:
Emp
City
Empid ,empName ,Salary
Empid, City

SELECT empname, fname, lname FROM employee WHERE empid IN (SELECT empid FROM city GROUP BY empid HAVING COUNT(empid) > 1)
8. Find all employees who is living in the same city. (table is same as above)
SELECT fname FROM employee
WHERE empid IN (SELECT empid FROM city a WHERE city IN (SELECT city FROM city b GROUP BY city HAVING COUNT(city) > 1))
9. There is a table named MovieTable with three columns – moviename, person and role. Write a query which gets the movie details where Mr. Amitabh and Mr. Vinod acted and their role is actor.
SELECT DISTINCT m1.moviename
FROM MovieTable m1 INNER JOIN
MovieTable m2
ON m1.moviename = m2.moviename
WHERE (m1.person = ‘amitabh’ AND m2.person = ‘vinod’
OR m2.person = ‘amitabh’ AND m1.person = ‘vinod’)
AND (m1.role = ‘actor’) AND (m2.role = ‘actor’) ORDER BY m1.moviename
10. There are two employee tables named emp1 and emp2. Both contains same structure (salary details). But Emp2 salary details are incorrect and emp1 salary details are correct. So, write a query which corrects salary details of the table emp2
update a set a.sal=b.sal from emp1 a, emp2 b where a.empid=b.empid
11. Given a Table named “Students” which contains studentid, subjectid and marks. Where there are 10 subjects and 50 students. Write a Query to find out the Maximum marks obtained in each subject.
In this same tables now write a SQL Query to get the studentid also to combine with previous results.
12. Three tables – student , course, marks – how do go at finding name of the students who got max marks in the diff courses.
SELECT student.name, course.name AS coursename, marks.sid, marks.mark
FROM marks
INNER JOIN student ON marks.sid = student.sid
INNER JOIN course ON marks.cid = course.cid
WHERE marks.mark = (SELECT MAX(Mark) FROM Marks MaxMark WHERE MaxMark.cID = Marks.cID)
13. There is a table day_temp which has three columns dayid, day and temperature. How do I write a query to get the difference of temperature among each other for seven days of a week? SELECT a.dayid, a.dday, a.tempe, (a.tempe – b.tempe) AS [Difference] FROM day_temp a INNER JOIN day_temp b ON a.dayid = b.dayid + 1
OR Select a.day, (a.degree-b.degree) as [Difference] from temperature a, temperature b where a.id=b.id+1
14. There is a table which contains the names like this. a1, a2, a3, a3, a4, a1, a1, a2 and their salaries. Write a query to get grand total salary, and total salaries of individual employees in one query. SELECT empid, SUM(salary) AS salary FROM emp GROUP BY empid WITH ROLLUP ORDER BY empid
15. How to know how many tables contains empno as a column in a database? SELECT COUNT(*) AS Counter FROM syscolumns WHERE (name = ’empno’)
16. Find duplicate rows in a table? OR I have a table with one column which has many records which are not distinct. I need to find the distinct values from that column and number of times it’s repeated. SELECT sid, mark, COUNT(*) AS Counter FROM marks GROUP BY sid, mark HAVING (COUNT(*) > 1)
17. How to delete the rows which are duplicate (don’t delete both duplicate records).
WITH numbered AS
(
SELECT
ROW_NUMBER() OVER (PARTITION BY keyvalue ORDER BY keyvalue) AS rowno,
keyvalue
FROM
#SampleTestData
)
DELETE FROM numbered
WHERE rowno > 1;
OR
SET ROWCOUNT 1
WHILE @@rowcount > 0
DELETE emp FROM emp a WHERE (SELECT COUNT(*) FROM emp b WHERE b.empid = a.empid AND b.empname = a.empname) > 1
SET ROWCOUNT 0
18. How to find 6th highest salary
SELECT TOP 1 salary FROM (SELECT DISTINCT TOP 6 salary FROM employee
ORDER BY salary DESC) a ORDER BY salary
19. Find top salary among two tables
SELECT TOP 1 sal FROM (SELECT MAX(sal) AS sal FROM sal1
UNION SELECT MAX(sal) AS sal FROM sal2) a ORDER BY sal DESC
20. FirstDay
Datepart
Abbreviations
Year
yy, yyyy
Quarter
qq, q
Month
mm, m
Dayofyear
dy, y
Day
dd, d
Week
wk, ww
weekday
dw
hour
hh
minute
mi, n
second
ss, s
millisecond
ms
21. Table A contains column1 which is primary key and has 2 values (1, 2) and Table B contains column1 which is primary key and has 2 values (2, 3). Write a query which returns the values that are not common for the tables and the query should return one column with 2 records.
SELECT tbla.a FROM tbla, tblb WHERE tbla.a <> (SELECT tblb.a FROM tbla, tblb
WHERE tbla.a = tblb.a) UNION SELECT tblb.a FROM tbla, tblb WHERE tblb.a <>
(SELECT tbla.a FROM tbla, tblb WHERE tbla.a = tblb.a)
OR (better approach) SELECT a FROM tbla WHERE a NOT IN (SELECT a FROM tblb)
UNION ALL SELECT a FROM tblb WHERE a NOT IN (SELECT a FROM tbla)
22. List all products with total quantity ordered, if quantity ordered is null show it as 0. SELECT name, CASE WHEN SUM(qty) IS NULL THEN 0 WHEN SUM(qty) > 0 THEN SUM(qty) END AS tot FROM [order] RIGHT OUTER JOIN product ON [order].prodid = product.prodid GROUP BY name
23. ANY, SOME, or ALL? ALL means greater than every value–in other words, greater than the maximum value. For example, >ALL (1, 2, 3) means greater than 3. ANY means greater than at least one value, that is, greater than the minimum. So >ANY (1, 2, 3) means greater than 1. SOME is an SQL-92 standard equivalent for ANY.
24. IN & = (difference in correlated sub query) INDEX
25. What is Index? It’s purpose? Indexes in databases are similar to indexes in books. In a database, an index allows the database program to find data in a table without scanning the entire table. An index in a database is a list of values in a table with the storage locations of rows in the table that contain each value. Indexes can be created on either a single column or a combination of columns in a table and are implemented in the form of B-trees. An index contains an entry with one or more columns (the search key) from each row in a table. A B-tree is sorted on the search key, and can be searched efficiently on any leading subset of the search key. For example, an index on columns A, B, C can be searched efficiently on A, on A, B, and A, B, C.
26. Explain about Clustered and non clustered index? How to choose between a Clustered Index and a Non-Clustered Index? There are clustered and nonclustered indexes. A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf nodes of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows. Consider using a clustered index for:
o Columns that contain a large number of distinct values.
o Queries that return a range of values using operators such as BETWEEN, >, >=, <, and <=.
o Columns that are accessed sequentially.
o Queries that return large result sets. Non-clustered indexes have the same B-tree structure as clustered indexes, with two significant differences:
o The data rows are not sorted and stored in order based on their non-clustered keys.
o The leaf layer of a non-clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows. Each index row contains the non-clustered key value and
one or more row locators that point to the data row (or rows if the index is not unique) having the key value.
o Per table only 249 non clustered indexes.
27. Disadvantage of index? Every index increases the time in takes to perform INSERTS, UPDATES and DELETES, so the number of indexes should not be very much. Also indexes increases storage space required.
28. Given a scenario that I have a 10 Clustered Index in a Table to all their 10 Columns. What are the advantages and disadvantages? A: Only 1 clustered index is possible. And More indexes will degrade the performance
29. How can I enforce to use particular index? You can use index hint (index=<index_name>) after the table name. SELECT au_lname FROM authors (index=aunmind)
30. What is Index Tuning? One of the hardest tasks facing database administrators is the selection of appropriate columns for non-clustered indexes. You should consider creating non-clustered indexes on any columns that are frequently referenced in the WHERE clauses of SQL statements. Other good candidates are columns referenced by JOIN and GROUP BY operations. You may wish to also consider creating non-clustered indexes that cover all of the columns used by certain frequently issued queries. These queries are referred to as “covered queries” and experience excellent performance gains. Index Tuning is the process of finding appropriate column for non-clustered indexes. SQL Server provides a wonderful facility known as the Index Tuning Wizard which greatly enhances the index selection process.
31. Difference between Index defrag and Index rebuild? When you create an index in the database, the index information used by queries is stored in index pages. The sequential index pages are chained together by pointers from one page to the next. When changes are made to the data that affect the index, the information in the index can become scattered in the database. Rebuilding an index reorganizes the storage of the index data (and table data in the case of a clustered index) to remove fragmentation. This can improve disk performance by reducing the number of page reads required to obtain the requested data DBCC INDEXDEFRAG – Defragments clustered and secondary indexes of the specified table or view. **
32. What is sorting and what is the difference between sorting & clustered indexes? The ORDER BY clause sorts query results by one or more columns up to 8,060 bytes. This will happen by the time when we retrieve data from database. Clustered indexes physically sorting data, while inserting/updating the table.
33. What are statistics, under what circumstances they go out of date, and how do you update them? Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query. Some situations under which you should update statistics: 1) If there is significant change in the key values in the index 2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated 3) Database is upgraded from a previous version
34. What is fill factor? What is the use of it? What happens when we ignore it? When you should use low fill factor?
When you create a clustered index, the data in the table is stored in the data pages of the database according to the order of the values in the indexed columns. When new rows of data are inserted into the table or the values in the indexed columns are changed, Microsoft® SQL Server™ 2000 may have to reorganize the storage of the data in the table to make room for the new row and maintain the ordered storage of the data. This also applies to nonclustered indexes. When data is added or changed, SQL Server may have to reorganize the storage of the data in the nonclustered index pages. When a new row is added to a full index page, SQL Server moves approximately half the rows to a new page to make room for the new row. This reorganization is known as a page split. Page splitting can impair performance and fragment the storage of the data in a table. When creating an index, you can specify a fill factor to leave extra gaps and reserve a percentage of free space on each leaf level page of the index to accommodate future expansion in the storage of the table’s data and reduce the potential for page splits. The fill factor value is a percentage from 0 to 100 that specifies how much to fill the data pages after the index are created. A value of 100 means the pages will be full and will take the least amount of storage space. This setting should be used only when there will be no changes to the data, for example, on a read-only table. A lower value leaves more empty space on the data pages, which reduces the need to split data pages as indexes grow but requires more storage space. This setting is more appropriate when there will be changes to the data in the table. DATA TYPES
35. What are the data types in SQL
Bigint
Binary
Bit
char
cursor
Datetime
Decimal
Float
image
int
Money
Nchar
Ntext
nvarchar
real
Smalldatetime
Smallint
smallmoney
text
timestamp
Tinyint
Varbinary
Varchar
uniqueidentifier
36. Difference between char and nvarchar / char and varchar data-type? char[(n)] – Fixed-length non-Unicode character data with length of n bytes. n must be a value from 1 through 8,000. Storage size is n bytes. The SQL-92 synonym for char is character. nvarchar(n) – Variable-length Unicode character data of n characters. n must be a value from 1 through 4,000. Storage size, in bytes, is two times the number of characters entered. The data entered can be 0 characters in length. The SQL-92 synonyms for nvarchar are national char varying and national character varying. varchar[(n)] – Variable-length non-Unicode character data with length of n bytes. n must be a value from 1 through 8,000. Storage size is the actual length in bytes of the data entered, not n bytes. The data entered can be 0 characters in length. The SQL-92 synonyms for varchar are char varying or character varying.
37. GUID datasize? 128bit
38. How GUID becoming unique across machines? To ensure uniqueness across machines, the ID of the network card is used (among others) to compute the number.
Creating and Modifying Identifier Columns
Only one identifier column and one globally unique identifier column can be created per table.
IDENTITY Property
Identifier columns can be implemented using the IDENTITY property, which allows the application developer to specify both an identity number for the first row inserted into the table (Identity Seed
property) and an increment (Identity Increment property) to be added to the seed to determine successive identity numbers. When inserting values into a table with an identifier column, Microsoft® SQL Server™ automatically generates the next identity value by adding the increment to the seed.
When you use the IDENTITY property to define an identifier column, consider that:
 A table can have only one column defined with the IDENTITY property, and that column must be defined using the decimal, int, numeric, smallint, or tinyint data type.
 The seed and increment can be specified. The default value for both is 1.
 The identifier column must not allow null values and must not contain a DEFAULT definition or object.
 The column can be referenced in a select list by using the IDENTITYCOL keyword after the IDENTITY property has been set.
 The OBJECTPROPERTY function can be used to determine if a table has an IDENTITY column, and the COLUMNPROPERTY function can be used to determine the name of the IDENTITY column.
Globally Unique Identifiers
Although the IDENTITY property automates row numbering within one table, separate tables, each with its own identifier column, can generate the same values. This is because the IDENTITY property is guaranteed to be unique only for the table on which it is used. If an application must generate an identifier column that is unique across the entire database, or every database on every networked computer in the world, use the ROWGUIDCOL property, the uniqueidentifier data type, and the NEWID function.
When you use the ROWGUIDCOL property to define a globally unique identifier column, consider that:
A table can have only one ROWGUIDCOL column, and that column must be defined using the uniqueidentifier data type.
SQL Server does not automatically generate values for the column. To insert a globally unique value, create a DEFAULT definition on the column that uses the NEWID function to generate a globally unique value.
The column can be referenced in a select list by using the ROWGUIDCOL keyword after the ROWGUIDCOL property has been set. This is similar to the way an IDENTITY column can be referenced using the IDENTITYCOL keyword.
The OBJECTPROPERTY function can be used to determine if a table has a ROWGUIDCOL column, and the COLUMNPROPERTY function can be used to determine the name of the ROWGUIDCOL column.
Because the ROWGUIDCOL property does not enforce uniqueness, the UNIQUE constraint should be used to ensure that unique values are inserted into the ROWGUIDCOL column.
Note If an identifier column exists for a table with frequent deletions, gaps can occur between identity values; deleted identity values are not reused. To avoid such gaps, do not use the IDENTITY property. Instead, you can create a trigger that determines a new identifier value, based on existing values in the identifier column, as rows are inserted.
39. What is the difference between text and image data type? Text and image. Use text for character data if you need to store more than 255 characters in SQL Server 6.5, or more than 8000 in SQL Server 7.0. Use image for binary large objects (BLOBs) such as digital images. With text and image data types, the data is not stored in the
row, so the limit of the page size does not apply.All that is stored in the row is a pointer to the database pages that contain the data.Individual text, ntext, and image values can be a maximum of 2-GB, which is too long to store in a single data row. JOINS
40. What are joins? Sometimes we have to select data from two or more tables to make our result complete. We have to perform a join.
41. How many types of Joins? Joins can be categorized as:
 Inner joins (the typical join operation, which uses some comparison operator like = or <>). These include equi-joins and natural joins. Inner joins use a comparison operator to match rows from two tables based on the values in common columns from each table. For example, retrieving all rows where the student identification number is the same in both the students and courses tables.
Outer joins. Outer joins can be a left, a right, or full outer join. Outer joins are specified with one of the following sets of keywords when they are specified in the FROM clause: LEFT JOIN or LEFT OUTER JOIN -The result set of a left outer join includes all the rows from the left table specified in the LEFT OUTER clause, not just the ones in which the joined columns match. When a row in the left table has no matching rows in the right table, the associated result set row contains null values for all select list columns coming from the right table.
RIGHT JOIN or RIGHT OUTER JOIN – A right outer join is the reverse of a left outer join. All rows from the right table are returned. Null values are returned for the left table any time a right table row has no matching row in the left table.
FULL JOIN or FULL OUTER JOIN – A full outer join returns all rows in both the left and right tables. Any time a row has no match in the other table, the select list columns from the other table contain null values. When there is a match between the tables, the entire result set row contains data values from the base tables.
Cross joins – Cross joins return all rows from the left table, each row from the left table is combined with all rows from the right table. Cross joins are also called Cartesian products. (A Cartesian join will get you a Cartesian product. A Cartesian join is when you join every row of one table to every row of another table. You can also get one by joining every row of a table to every row of itself.)
What is self join? A table can be joined to itself in a self-join.
What are the differences between UNION and JOINS? A join selects columns from 2 or more tables. A union selects rows.
Can I improve performance by using the ANSI-style joins instead of the old-style joins? Code Example 1: select o.name, i.name from sysobjects o, sysindexes i where o.id = i.id Code Example 2: select o.name, i.name from sysobjects o inner join sysindexes i on o.id = i.id You will not get any performance gain by switching to the ANSI-style JOIN syntax. Using the ANSI-JOIN syntax gives you an important advantage: Because the join logic is cleanly separated from the filtering criteria, you can understand the query logic more quickly.
The SQL Server old-style JOIN executes the filtering conditions before executing the joins, whereas the ANSI-style JOIN reverses this procedure (join logic precedes filtering). Perhaps the most compelling argument for switching to the ANSI-style JOIN is that Microsoft has explicitly stated that SQL Server will not support the old-style OUTER JOIN syntax indefinitely. Another important consideration is that the ANSI-style JOIN supports query constructions that the old-style JOIN syntax does not support.
What is derived table?
Derived tables are SELECT statements in the FROM clause referred to by an alias or a user-specified name. The result set of the SELECT in the FROM clause forms a table used by the outer SELECT statement. For example, this SELECT uses a derived table to find if any store carries all book titles in the pubs database:
SELECT ST.stor_id, ST.stor_name FROM stores AS ST,
(SELECT stor_id, COUNT(DISTINCT title_id) AS title_count FROM sales GROUP BY stor_id) AS SA WHERE ST.stor_id = SA.stor_id AND SA.title_count = (SELECT COUNT(*) FROM titles)
STORED PROCEDURE
What is stored procedure?
A stored procedure is a set of Structured Query Language (SQL) statements that you assign a name to and store in a database in compiled form so that you can share it between a number of programs.
They allow modular programming.
They allow faster execution.
They can reduce network traffic.
They can be used as a security mechanism.
What are the different types of Storage Procedure?
. Temporary Stored Procedures – SQL Server supports two types of temporary procedures: local and global. A local temporary procedure is visible only to the connection that created it. A global temporary procedure is available to all connections. Local temporary procedures are automatically dropped at the end of the current session. Global temporary procedures are dropped at the end of the last session using the procedure. Usually, this is when the session that created the procedure ends. Temporary procedures named with # and ## can be created by any user.
a. System stored procedures are created and stored in the master database and have the sp_ prefix.(or xp_) System stored procedures can be executed from any database without having to qualify the stored procedure name fully using the database name master. (If any user-created stored procedure has the same name as a system stored procedure, the user-created stored procedure will never be executed.)
b. Automatically Executing Stored Procedures – One or more stored procedures can execute automatically when SQL Server starts. The stored procedures must be created by the system administrator and executed under the sysadmin fixed server role as a background process. The procedure(s) cannot have any input parameters.
c. User stored procedure
How will know whether the SQL statements are executed?
When used in a stored procedure, the RETURN statement can specify an integer value to return to the calling application, batch, or procedure. If no value is specified on RETURN, a stored procedure returns the value 0. The stored procedures return a value of 0 when no errors were encountered. Any nonzero value indicates an error occurred.
Why one should not prefix user stored procedures with sp_?
It is strongly recommended that you do not create any stored procedures using sp_ as a prefix. SQL Server always looks for a stored procedure beginning with sp_ in this order:
0. The stored procedure in the master database.
1. The stored procedure based on any qualifiers provided (database name or owner).
2. The stored procedure using dbo as the owner, if one is not specified.
Therefore, although the user-created stored procedure prefixed with sp_ may exist in the current database, the master database is always checked first, even if the stored procedure is qualified with the database name.
What can cause a stored procedure execution plan to become invalidated and/or fall out of cache?
0. Server restart
1. Plan is aged out due to low use
2. DBCC FREEPROCCACHE (sometime desired to force it)
When do one need to recompile stored procedure? if a new index is added from which the stored procedure might benefit, optimization does not automatically happen (until the next time the stored procedure is run after SQL Server is restarted).
SQL Server provides three ways to recompile a stored procedure:
The sp_recompile system stored procedure forces a recompile of a stored procedure the next time it is run.
Creating a stored procedure that specifies the WITH RECOMPILE option in its definition indicates that SQL Server does not cache a plan for this stored procedure; the stored procedure is recompiled each time it is executed. Use the WITH RECOMPILE option when stored procedures take parameters whose values differ widely between executions of the stored procedure, resulting in different execution plans to be created each time. Use of this option is uncommon, and causes the stored procedure to execute more slowly because the stored procedure must be recompiled each time it is executed.
You can force the stored procedure to be recompiled by specifying the WITH RECOMPILE option when you execute the stored procedure. Use this option only if the parameter you are supplying is atypical or if the data has significantly changed since the stored procedure was created.
How to find out which stored procedure is recompiling? How to stop stored procedures from recompiling?
I have Two Stored Procedures SP1 and SP2 as given below. How the Transaction works, whether SP2 Transaction succeeds or fails? CREATE PROCEDURE SP1 AS BEGIN TRAN INSERT INTO MARKS (SID,MARK,CID) VALUES (5,6,3) EXEC SP2 ROLLBACK GO CREATE PROCEDURE SP2 AS BEGIN TRAN INSERT INTO MARKS (SID,MARK,CID) VALUES (100,100,103) commit tran GO Both will get roll backed.
CREATE PROCEDURE SP1 AS BEGIN TRAN INSERT INTO MARKS (SID,MARK,CID) VALUES (5,6,3) BEGIN TRAN INSERT INTO STUDENT (SID,NAME1) VALUES (1,’SA’) commit tran ROLLBACK TRAN GO Both will get roll backed.
How will you handle Errors in Sql Stored Procedure?
INSERT NonFatal VALUES (@Column2) IF @@ERROR <>0 BEGIN PRINT ‘Error Occured’ END http://www.sqlteam.com/item.asp?ItemID=2463
How will you raise an error in sql?
RAISERROR – Returns a user-defined error message and sets a system flag to record that an error has occurred. Using RAISERROR, the client can either retrieve an entry from the sysmessages table or build a message dynamically with user-specified severity and state information. After the message is defined it is sent back to the client as a server error message.
Returns a user-defined error message and sets a system flag to record that an error has occurred. Using RAISERROR, the client can either retrieve an entry from the sysmessages table or build a message dynamically with user-specified severity and state information. After the message is defined it is sent back to the client as a server error message.
Syntax
RAISERROR ({msg_id | msg_str}{, severity, state} [, argument [,…n]] ) [WITH option[,…n]] Arguments
msg_id
Is a user-defined error message stored in the sysmessages table. Error numbers for user-defined error messages should be greater than 50,000. Ad hoc messages raise an error of 50,000. The maximum value for msg_id is 2,147,483,647 (2 (31) – 1).
msg_str
Is an ad hoc message with formatting similar to the PRINTF format style used in C. The error message can have as many as 8,000 characters. All ad hoc messages have a standard message ID of 14,000.
This format is supported for msg_str:
% [[flag] [width] [precision] [{h | l}]] type
The parameters that can be used in msg_str are:
flag
Is a code that determines the spacing and justification of the user-defined error message.
I have a stored procedure like commit tran create table a() insert into table b — — rollback tran what will be the result? Is table created? data will be inserted in table b?
What do you do when one procedure is blocking the other? **
How you will return XML from Stored Procedure? You use the FOR XML clause of the SELECT statement, and within the FOR XML clause you specify an XML mode: RAW, AUTO, or EXPLICIT.
What are the differences between RAW, AUTO and Explicit modes in retrieving data from SQL Server in XML format? **
Can a Stored Procedure call itself (recursive). If so then up to what level and can it be control? Stored procedures are nested when one stored procedure calls another. You can nest stored procedures up to 32 levels. The nesting level increases by one when the called stored procedure begins execution and decreases by one when the called stored procedure completes execution. Attempting to exceed the maximum of 32 levels of nesting causes the whole calling stored procedure chain to fail. The current nesting level for the stored procedures in execution is stored in the @@NESTLEVEL function. eg: SET NOCOUNT ON USE master IF OBJECT_ID(‘dbo.sp_calcfactorial’) IS NOT NULL DROP PROC dbo.sp_calcfactorial GO CREATE PROC dbo.sp_calcfactorial @base_number int, @factorial int OUT AS DECLARE @previous_number int IF (@base_number<2) SET @factorial=1 — Factorial of 0 or 1=1 ELSE BEGIN SET @previous_number=@base_number-1 EXEC dbo.sp_calcfactorial @previous_number, @factorial OUT — Recursive call IF (@factorial=-1) RETURN(-1) — Got an error, return SET @factorial=@factorial*@base_number END RETURN(0) GO calling proc. DECLARE @factorial int EXEC dbo.sp_calcfactorial 4, @factorial OUT SELECT @factorial
Nested Triggers Triggers are nested when a trigger performs an action that initiates another trigger, which can initiate another trigger, and so on. Triggers can be nested up to 32 levels, and you can control whether triggers can be nested through the nested triggers server configuration option.
What is an extended stored procedure? Can you instantiate a COM object by using T-SQL? An extended stored procedure is a function within a DLL (written in a programming language like C, C++ using Open Data Services (ODS) API) that can be called from T-SQL, just the way we call normal stored procedures using the EXEC statement.
Difference between view and stored procedure? Views can have only select statements (create, update, truncate, delete statements are not allowed) Views cannot have “select into”, “Group by” “Having”, ”Order by”
What is a Function & what are the different user defined functions? Function is a saved Transact-SQL routine that returns a value. User-defined functions cannot be used to perform a set of actions that modify the global database state. User-defined functions, like system
functions, can be invoked from a query. They also can be executed through an EXECUTE statement like stored procedures.
0. Scalar Functions Functions are scalar-valued if the RETURNS clause specified one of the scalar data types
1. Inline Table-valued Functions If the RETURNS clause specifies TABLE with no accompanying column list, the function is an inline function.
2. Multi-statement Table-valued Functions If the RETURNS clause specifies a TABLE type with columns and their data types, the function is a multi-statement table-valued function.
What are the difference between a function and a stored procedure?
0. Functions can be used in a select statement where as procedures cannot
1. Procedure takes both input and output parameters but Functions takes only input parameters
2. Functions cannot return values of type text, ntext, image & timestamps where as procedures can
3. Functions can be used as user defined datatypes in create table but procedures cannot ***Eg:-create table <tablename>(name varchar(10),salary getsal(name)) Here getsal is a user defined function which returns a salary type, when table is created no storage is allotted for salary type, and getsal function is also not executed, But when we are fetching some values from this table, getsal function get’s executed and the return Type is returned as the result set.
How to debug a stored procedure? TRIGGER
What is Trigger? What is its use? What are the types of Triggers? What are the new kinds of triggers in sql 2000? Triggers are a special class of stored procedure defined to execute automatically when an UPDATE, INSERT, or DELETE statement is issued against a table or view. Triggers are powerful tools that sites can use to enforce their business rules automatically when data is modified. The CREATE TRIGGER statement can be defined with the FOR UPDATE, FOR INSERT, or FOR DELETE clauses to target a trigger to a specific class of data modification actions. When FOR UPDATE is specified, the IF UPDATE (column_name) clause can be used to target a trigger to updates affecting a particular column. You can use the FOR clause to specify when a trigger is executed:
 AFTER (default) – The trigger executes after the statement that triggered it completes. If the statement fails with an error, such as a constraint violation or syntax error, the trigger is not executed. AFTER triggers cannot be specified for views.
 INSTEAD OF -The trigger executes in place of the triggering action. INSTEAD OF triggers can be specified on both tables and views. You can define only one INSTEAD OF trigger for each triggering action (INSERT, UPDATE, and DELETE). INSTEAD OF triggers can be used to perform enhance integrity checks on the data values supplied in INSERT and UPDATE statements. INSTEAD OF triggers also let you specify actions that allow views, which would normally not support updates, to be updatable. An INSTEAD OF trigger can take actions such as:
 Ignoring parts of a batch.
 Not processing a part of a batch and logging the problem rows.
 Taking an alternative action if an error condition is encountered.
In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there’s no way to control the order in which
the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder. Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also.
When should one use “instead of Trigger”? Example CREATE TABLE BaseTable ( PrimaryKey int IDENTITY(1,1), Color nvarchar(10) NOT NULL, Material nvarchar(10) NOT NULL, ComputedCol AS (Color + Material) ) GO –Create a view that contains all columns from the base table. CREATE VIEW InsteadView AS SELECT PrimaryKey, Color, Material, ComputedCol FROM BaseTable GO –Create an INSTEAD OF INSERT trigger on tthe view. CREATE TRIGGER InsteadTrigger on InsteadView INSTEAD OF INSERT AS BEGIN –Build an INSERT statement ignoring inserrted.PrimaryKey and –inserted.ComputedCol. INSERT INTO BaseTable SELECT Color, Material FROM inserted END GO — can insert value to basetable by this insert into basetable(color,material) values (‘red’,’abc’) — insert into InsteadView(color,material)) values (‘red’,’abc’) can’t do this. — It will give error “‘PrimaryKey’ iin table ‘InsteadView’ cannot be null.” — can insert value through table by this< insert into InsteadView values (1,’red’,’abc’,1) –PrimaryKey, ComputedCol wont take values from here
Difference between trigger and stored procedure? Trigger will get execute automatically when an UPDATE, INSERT, or DELETE statement is issued against a table or view. We have to call stored procedure manually, or it can execute automatic when the SQL Server starts (You can use the sp_procoption system stored procedure to mark the stored procedure to automatic execution when the SQL Server will start.
The following trigger generates an e-mail whenever a new title is added. CREATE TRIGGER reminder ON titles FOR INSERT AS EXEC master..xp_sendmail ‘MaryM’, ‘New title, mention in the next report to distributors.’
Drawback of trigger? Its alternative solution? Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster. LOCK
What are locks? Microsoft® SQL Server™ 2000 uses locking to ensure transactional integrity and database consistency. Locking prevents users from reading data being changed by other users, and prevents
multiple users from changing the same data at the same time. If locking is not used, data within the database may become logically incorrect, and queries executed against that data may produce unexpected results.
What are the different types of locks? SQL Server uses these resource lock modes.
Lock mode
Description
Shared (S)
Used for operations that do not change or update data (read-only operations), such as a SELECT statement.
Update (U)
Used on resources that can be updated. Prevents a common form of deadlock that occurs when multiple sessions are reading, locking, and potentially updating resources later.
Exclusive (X)
Used for data-modification operations, such as INSERT, UPDATE, or DELETE. Ensures that multiple updates cannot be made to the same resource at the same time.
Intent
Used to establish a lock hierarchy. The types of intent locks are: intent shared (IS), intent exclusive (IX), and shared with intent exclusive (SIX).
Schema
Used when an operation dependent on the schema of a table is executing. The types of schema locks are: schema modification (Sch-M) and schema stability (Sch-S).
Bulk Update (BU)
Used when bulk-copying data into a table and the TABLOCK hint is specified.
What is a dead lock? Give a practical sample? How you can minimize the deadlock situation? What is a deadlock and what is a live lock? How will you go about resolving deadlocks? Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other’s piece. Each process would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user’s process. A livelock is one, where a request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further shared locks. (A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely.)
What is isolation level? An isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. A lower isolation level increases concurrency, but at the expense of data correctness. Conversely, a higher isolation level ensures that data is correct, but can affect concurrency negatively. The isolation level required by an application determines the locking behavior SQL Server uses. SQL-92 defines the following isolation levels, all of which are supported by SQL Server:
 Read uncommitted (the lowest level where transactions are isolated only enough to ensure that physically corrupt data is not read).
 Read committed (SQL Server default level).
 Repeatable read.
 Serializable (the highest level, where transactions are completely isolated from one another).
Isolation level
Dirty read
Nonrepeatable read
Phantom
Read uncommitted
Yes
Yes
Yes
Read committed
No
Yes
Yes
Repeatable read
No
No
Yes
Serializable
No
No
No
Uncommitted Dependency (Dirty Read) – Uncommitted dependency occurs when a second transaction selects a row that is being updated by another transaction. The second transaction is
reading data that has not been committed yet and may be changed by the transaction updating the row. For example, an editor is making changes to an electronic document. During the changes, a second editor takes a copy of the document that includes all the changes made so far, and distributes the document to the intended audience. Inconsistent Analysis (Nonrepeatable Read) Inconsistent analysis occurs when a second transaction accesses the same row several times and reads different data each time. Inconsistent analysis is similar to uncommitted dependency in that another transaction is changing the data that a second transaction is reading. However, in inconsistent analysis, the data read by the second transaction was committed by the transaction that made the change. Also, inconsistent analysis involves multiple reads (two or more) of the same row and each time the information is changed by another transaction; thus, the term nonrepeatable read. For example, an editor reads the same document twice, but between each reading, the writer rewrites the document. When the editor reads the document for the second time, it has changed. Phantom Reads Phantom reads occur when an insert or delete action is performed against a row that belongs to a range of rows being read by a transaction. The transaction’s first read of the range of rows shows a row that no longer exists in the second or succeeding read, as a result of a deletion by a different transaction. Similarly, as the result of an insert by a different transaction, the transaction’s second or succeeding read shows a row that did not exist in the original read. For example, an editor makes changes to a document submitted by a writer, but when the changes are incorporated into the master copy of the document by the production department, they find that new unedited material has been added to the document by the author. This problem could be avoided if no one could add new material to the document until the editor and production department finish working with the original document.
What is the difference between the REPEATABLE READ and SERIALIZE isolation levels?
Locking Hints – A range of table-level locking hints can be specified using the SELECT, INSERT, UPDATE, and DELETE statements to direct Microsoft® SQL Server 2000 to the type of locks to be used. Table-level locking hints can be used when a finer control of the types of locks acquired on an object is required. These locking hints override the current transaction isolation level for the session.
Locking hint
Description
HOLDLOCK
Hold a shared lock until completion of the transaction instead of releasing the lock as soon as the required table, row, or data page is no longer required. HOLDLOCK is equivalent to SERIALIZABLE.
NOLOCK
Do not issue shared locks and do not honor exclusive locks. When this option is in effect, it is possible to read an uncommitted transaction or a set of pages that are rolled back in the middle of a read. Dirty reads are possible. Only applies to the SELECT statement.
PAGLOCK
Use page locks where a single table lock would usually be taken.
READCOMMITTED
Perform a scan with the same locking semantics as a transaction running at the READ COMMITTED isolation level. By default, SQL Server 2000 operates at this isolation level.
READPAST
Skip locked rows. This option causes a transaction to skip rows locked by other transactions that would ordinarily appear in the result set, rather than block the transaction waiting for the other transactions to release their locks on these rows. The READPAST lock hint applies only to transactions operating at READ COMMITTED isolation and will read only past row-level locks. Applies only to the SELECT statement.
READUNCOMMITTED
Equivalent to NOLOCK.
REPEATABLEREAD
Perform a scan with the same locking semantics as a transaction running at the REPEATABLE READ isolation level.
ROWLOCK
Use row-level locks instead of the coarser-grained page- and table-level locks.
SERIALIZABLE
Perform a scan with the same locking semantics as a transaction running at the SERIALIZABLE isolation level. Equivalent to HOLDLOCK.
TABLOCK
Use a table lock instead of the finer-grained row- or page-level locks. SQL Server holds this lock until the end of the statement. However, if you also specify HOLDLOCK, the lock is held until the end of the transaction.
TABLOCKX
Use an exclusive lock on a table. This lock prevents others from reading or updating the table and is held until the end of the statement or transaction.
UPDLOCK
Use update locks instead of shared locks while reading a table, and hold locks until the end of the statement or transaction. UPDLOCK has the advantage of allowing you to read data (without blocking other readers) and update it later with the assurance that the data has not changed since you last read it.
XLOCK
Use an exclusive lock that will be held until the end of the transaction on all data processed by the statement. This lock can be specified with either PAGLOCK or TABLOCK, in which case the exclusive lock applies to the appropriate level of granularity.
For example, if the transaction isolation level is set to SERIALIZABLE, and the table-level locking hint NOLOCK is used with the SELECT statement, key-range locks typically used to maintain serializable transactions are not taken. USE pubs GO SET TRANSACTION ISOLATION LEVEL SERIALIZABLE GO BEGIN TRANSACTION SELECT au_lname FROM authors WITH (NOLOCK) GO
What is escalation of locks? Lock escalation is the process of converting a lot of low level locks (like row locks, page locks) into higher level locks (like table locks). Every lock is a memory structure too many locks would mean, more memory being occupied by locks. To prevent this from happening, SQL Server escalates the many fine-grain locks to fewer coarse-grain locks. Lock escalation threshold was definable in SQL Server 6.5, but from SQL Server 7.0 onwards it’s dynamically managed by SQL Server. VIEW
What is View? Use? Syntax of View? A view is a virtual table made up of data from base tables and other views, but not stored separately.
 Views simplify users perception of the database (can be used to present only the necessary information while hiding details in underlying relations)
 Views improve data security preventing undesired accesses
 Views facilite the provision of additional data independence
Does the View occupy memory space? No
Can u drop a table if it has a view? Views or tables participating in a view created with the SCHEMABINDING clause cannot be dropped. If the view is not created using SCHEMABINDING, then we can drop the table.
Why doesn’t SQL Server permit an ORDER BY clause in the definition of a view? SQL Server excludes an ORDER BY clause from a view to comply with the ANSI SQL-92 standard. Because analyzing the rationale for this standard requires a discussion of the underlying structure of the structured query language (SQL) and the mathematics upon which it is based, we can’t fully explain the restriction here. However, if you need to be able to specify an ORDER BY clause in a view, consider using the following workaround: USE pubs GO CREATE VIEW AuthorsByName AS SELECT TOP 100 PERCENT * FROM authors ORDER BY au_lname, au_fname GO The TOP construct, which Microsoft introduced in SQL Server 7.0, is most useful when you combine it with the ORDER BY clause. The only time that SQL Server supports an ORDER BY clause in a view is when it is used in conjunction with the TOP keyword. (Note that the TOP keyword is a SQL Server extension to the ANSI SQL-92 standard.) TRANSACTION
What is Transaction? A transaction is a sequence of operations performed as a single logical unit of work. A logical unit of work must exhibit four properties, called the ACID (Atomicity, Consistency, Isolation, and Durability) properties, to qualify as a transaction:
 Atomicity – A transaction must be an atomic unit of work; either all of its data modifications are performed or none of them is performed.
 Consistency – When completed, a transaction must leave all data in a consistent state. In a relational database, all rules must be applied to the transaction’s modifications to maintain all data integrity. All internal data structures, such as B-tree indexes or doubly-linked lists, must be correct at the end of the transaction.
 Isolation – Modifications made by concurrent transactions must be isolated from the modifications made by any other concurrent transactions. A transaction either sees data in the state it was in before another concurrent transaction modified it, or it sees the data after the second transaction has completed, but it does not see an intermediate state. This is referred to as serializability because it results in the ability to reload the starting data and replay a series of transactions to end up with the data in the same state it was in after the original transactions were performed.
 Durability – After a transaction has completed, its effects are permanently in place in the system. The modifications persist even in the event of a system failure.
After one Begin Transaction a truncate statement and a RollBack statements are there. Will it be rollbacked? Since the truncate statement does not perform logged operation how does it RollBack? It will rollback. **
Given a SQL like Begin Tran Select @@Rowcount Begin Tran Select @@Rowcount Begin Tran Select @@Rowcount Commit Tran
Select @@Rowcount RollBack Select @@Rowcount RollBack Select @@Rowcount What is the value of @@Rowcount at each stmt levels? Ans : 0 – zero. @@ROWCOUNT – Returns the number of rows affected by the last statement. @@TRANCOUNT – Returns the number of active transactions for the current connection. Each Begin Tran will add count, each commit will reduce count and ONE rollback will make it 0. OTHER
What are the constraints for Table Constraints define rules regarding the values allowed in columns and are the standard mechanism for enforcing integrity. SQL Server 2000 supports five classes of constraints. NOT NULL CHECK UNIQUE PRIMARY KEY FOREIGN KEY
There are 50 columns in a table. Write a query to get first 25 columns Ans: Need to mention each column names.
How to list all the tables in a particular database? USE pubs GO sp_help
What are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors? Cursors allow row-by-row processing of the result sets. Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Further, there are restrictions on the SELECT statements that can be used with some types of cursors. How to avoid cursor:
0. Most of the times, set based operations can be used instead of cursors. Here is an example: If you have to give a flat hike to your employees using the following criteria: Salary between 30000 and 40000 — 5000 hike Salary between 40000 and 55000 — 7000 hike Salary between 55000 and 65000 — 9000 hike In this situation many developers tend to use a cursor, determine each employee’s salary and update his salary according to the above formula. But the same can be achieved by multiple update statements or can be combined in a single UPDATE statement as shown below: UPDATE tbl_emp SET salary = CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000 WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000 WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000 END
1. You need to call a stored procedure when a column in a particular row meets certain condition. You don’t have to use cursors for this. This can be achieved using WHILE loop, as long as there is a unique key to identify each row. For examples of using WHILE loop
for row by row processing, check out the ‘My code library’ section of my site or search for WHILE.
What is Dynamic Cursor? Suppose, I have a dynamic cursor attached to table in a database. I have another means by which I will modify the table. What do you think will the values in the cursor be? Dynamic cursors reflect all changes made to the rows in their result set when scrolling through the cursor. The data values, order, and membership of the rows in the result set can change on each fetch. All UPDATE, INSERT, and DELETE statements made by all users are visible through the cursor. Updates are visible immediately if they are made through the cursor using either an API function such as SQLSetPos or the Transact-SQL WHERE CURRENT OF clause. Updates made outside the cursor are not visible until they are committed, unless the cursor transaction isolation level is set to read uncommitted.
What is DATEPART? Returns an integer representing the specified datepart of the specified date.
Difference between Delete and Truncate?
TRUNCATE TABLE is functionally identical to DELETE statement with no WHERE clause: both remove all rows in the table. (1) But TRUNCATE TABLE is faster and uses fewer system and transaction log resources than DELETE. The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log. (2) Because TRUNCATE TABLE is not logged, it cannot activate a trigger. (3) The counter used by an identity for new rows is reset to the seed for the column. If you want to retain the identity counter, use DELETE instead. Of course, TRUNCATE TABLE can be rolled back.
Given a scenario where two operations, Delete Stmt and Truncate Stmt, where the Delete Statement was successful and the truncate stmt was failed. – Can u judge why?
What are global variables? Tell me some of them? Transact-SQL global variables are a form of function and are now referred to as functions. ABS – Returns the absolute, positive value of the given numeric expression. SUM AVG AND
What is DDL? Data definition language (DDL) statements are SQL statements that support the definition or declaration of database objects (for example, CREATE TABLE, DROP TABLE, and ALTER TABLE). You can use the ADO Command object to issue DDL statements. To differentiate DDL statements from a table or stored procedure name, set the CommandType property of the Command object to adCmdText. Because executing DDL queries with this method does not generate any recordsets, there is no need for a Recordset object.
What is DML? Data Manipulation Language (DML), which is used to select, insert, update, and delete data in the objects defined using DDL
What are keys in RDBMS? What is a primary key/ foreign key? There are two kinds of keys. A primary key is a set of columns from a table that are guaranteed to have unique values for each row of that table. Foreign keys are attributes of one table that have matching values in a primary key in another table, allowing for relationships between tables.
What is the difference between Primary Key and Unique Key? Both primary key and unique key enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered
index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only. There can be only one primary key on a table but unique keys can be multiple on a table
Define candidate key, alternate key, composite key? A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys. A key formed by combining at least two or more columns is called composite key.
What is the Referential Integrity? Referential integrity refers to the consistency that must be maintained between primary and foreign keys, i.e. every foreign key value must have a corresponding primary key value.
What are defaults? Is there a column to which a default can’t be bound? A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can’t have defaults bound to them.
What is the use of trace utility? **
What is the use of shell commands? xp_cmdshell Executes a given command string as an operating-system command shell and returns any output as rows of text. Grants nonadministrative users permissions to execute xp_cmdshell.
What is use of shrink database? Microsoft® SQL Server 2000 allows each file within a database to be shrunk to remove unused pages. Both data and transaction log files can be shrunk.
If the performance of the query suddenly decreased where you will check?
What is a pass-through query?
OpenRowset is a pass-through query. Microsoft® SQL Server 2000 sends pass-through queries as un-interpreted query strings to an OLE DB data source. The query must be in a syntax the OLE DB data source will accept. A Transact-SQL statement uses the results from a pass-through query as though it is a regular table reference. This example uses a pass-through query to retrieve a result set from a Microsoft Access version of the Northwind sample database. SELECT * FROM OpenRowset(‘Microsoft.Jet.OLEDB.4.0’, ‘c:northwind.mdb’;’admin’; ”, ‘SELECT CustomerID, CompanyName FROM Customers WHERE Region = ”WA” ‘)
How do you differentiate Local and Global Temporary table? You can create local and global temporary tables. Local temporary tables are visible only in the current session; global temporary tables are visible to all sessions. Prefix local temporary table names with single number sign (#table_name), and prefix global temporary table names with a double number sign (##table_name). SQL statements reference the temporary table using the value specified for table_name in the CREATE TABLE statement: CREATE TABLE #MyTempTable (cola INT PRIMARY KEY) INSERT INTO #MyTempTable VALUES (1)
How the Exists keyword works in SQL Server? USE pubs SELECT au_lname, au_fname FROM authors WHERE exists (SELECT * FROM publishers WHERE authors.city = publishers.city) When a subquery is introduced with the keyword EXISTS, it functions as an existence test. The WHERE clause of the outer query tests for the existence of rows returned by the subquery. The subquery does not actually produce any data; it returns a value of TRUE or FALSE.
ANY? USE pubs
SELECT au_lname, au_fname FROM authors WHERE city = ANY (SELECT city FROM publishers)
to select date part only SELECT CONVERT(char(10),GetDate(),101) –to select time part only SELECT right(GetDate(),7)
How can I send a message to user from the SQL Server? You can use the xp_cmdshell extended stored procedure to run net send command. This is the example to send the ‘Hello’ message to JOHN: EXEC master..xp_cmdshell “net send JOHN ‘Hello'” To get net send message on the Windows 9x machines, you should run the WinPopup utility. You can place WinPopup in the Startup group under Program Files.
What is normalization? Explain different levels of normalization? Explain Third normalization form with an example? The process of refining tables, keys, columns, and relationships to create an efficient database is called normalization. This should eliminates unnecessary duplication and provides a rapid search path to all necessary information. Some of the benefits of normalization are:
 Data integrity (because there is no redundant, neglected data)
 Optimized queries (because normalized tables produce rapid, efficient joins)
 Faster index creation and sorting (because the tables have fewer columns)
 Faster UPDATE performance (because there are fewer indexes per table)
 Improved concurrency resolution (because table locks will affect less data)
 Eliminate redundancy
There are a few rules for database normalization. Each rule is called a “normal form.” If the first rule is observed, the database is said to be in “first normal form.” If the first three rules are observed, the database is considered to be in “third normal form.” Although other levels of normalization are possible, third normal form is considered the highest level necessary for most applications.
6. First Normal Form (1NF)
 Eliminate repeating groups in individual tables
 Create a separate table for each set of related data.
 Identify each set of related data with a primary key.
Do not use multiple fields in a single table to store similar data. Example
Subordinate1
Subordinate2
Subordinate3
Subordinate4
Bob
Jim
Mary
Beth
Mary
Mike
Jason
Carol
Mark
Jim
Alan
Eliminate duplicative columns from the same table. Clearly, the Subordinate1-Subordinate4 columns are duplicative. What happens when we need to add or remove a subordinate?
Subordinates
Bob
Jim, Mary, Beth
Mary
Mike, Jason, Carol, Mark
Jim
Alan
This solution is closer, but it also falls short of the mark. The subordinates column is still duplicative and non-atomic. What happens when we need to add or remove a subordinate? We need to read and write the entire contents of the table. That’s not a big deal in this situation, but what if one manager had one hundred employees? Also, it complicates the process of selecting data from the database in future queries. Solution:
Subordinate
Bob
Jim
Bob
Mary
Bob
Beth
Mary
Mike
Mary
Jason
Mary
Carol
Mary
Mark
Jim
Alan
7. Second Normal Form (2NF)
 Create separate tables for sets of values that apply to multiple records.
 Relate these tables with a foreign key.
Records should not depend on anything other than a table’s primary key (a compound key, if necessary). For example, consider a customer’s address in an accounting system. The address is needed by the Customers table, but also by the Orders, Shipping, Invoices, Accounts Receivable, and Collections tables. Instead of storing the customer’s address as a separate entry in each of these tables, store it in one place, either in the Customers table or in a separate Addresses table.
8. Third Normal Form (3NF)
 Eliminate fields that do not depend on the key.
Values in a record that are not part of that record’s key do not belong in the table. In general, any time the contents of a group of fields may apply to more than a single record in the table, consider placing those fields in a separate table. For example, in an Employee Recruitment table, a candidate’s university name and address may be included. But you need a complete list of universities for group mailings. If university information is stored in the Candidates table, there is no way to list universities with no current candidates. Create a separate Universities table and link it to the Candidates table with a university code key. Another Example :
MemberId
Name
Company
CompanyLoc
1
John Smith
ABC
Alabama
2
Dave Jones
MCI
Florida
The Member table satisfies first normal form – it contains no repeating groups. It satisfies second normal form – since it doesn’t have a multivalued key. But the key is MemberID, and the company name and location describe only a company, not a member. To achieve third normal form, they must be moved into a separate table. Since they describe a company, CompanyCode becomes the key of the new “Company” table.
The motivation for this is the same for second normal form: we want to avoid update and delete anomalies. For example, suppose no members from the IBM were currently stored in the database. With the previous design, there would be no record of its existence, even though 20 past members were from IBM! Member Table
MemberId
Name
CID
1
John Smith
1
2
Dave Jones
2
Company Table
CId
Name
Location
1
ABC
Alabama
2
MCI
Florida
9. Boyce-Codd Normal Form (BCNF) A relation is in Boyce/Codd normal form if and only if the only determinants are candidate key. Its a different version of 3NF, indeed, was meant to replace it. [A determinant is any attribute on which some other attribute is (fully) functionally dependent.] 10. 4th Normal Form (4NF) A table is in 4NF if it is in BCNF and if it has no multi-valued dependencies. This applies primarily to key-only associative tables, and appears as a ternary relationship, but has incorrectly merged 2 distinct, independent relationships. Eg: This could be any 2 M:M relationships from a single entity. For instance, a member could know many software tools, and a software tool may be used by many members. Also, a member could have recommended many books, and a book could be recommended by many members.
Software
Member
Book
11. The correct solution, to cause the model to be in 4th normal form, is to ensure that all M:M relationships are resolved independently if they are indeed independent.
Software
membersoftware
member
memberBook
book
12. 5th Normal Form (5NF)(PJNF) A table is in 5NF, also called “Projection-Join Normal Form”, if it is in 4NF and if every join dependency in the table is a consequence of the candidate keys of the table.
13. Domain/key normal form (DKNF). A key uniquely identifies each row in a table. A domain is the set of permissible values for an attribute. By enforcing key and domain restrictions, the database is assured of being freed from modification anomalies. DKNF is the normalization level that most designers aim to achieve.
** Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it must first fulfill all the criteria of a 1NF database.
If a database is normalized by 3 NF then how many number of tables it should contain in minimum? How many minimum if 2NF and 1 NF?
What is denormalization and when would you go for it? As the name indicates, denormalization is the reverse process of normalization. It’s the controlled introduction of redundancy in to the database design. It helps improve the query performance as the number of joins could be reduced.
How can I randomly sort query results? To randomly order rows, or to return x number of randomly chosen rows, you can use the RAND function inside the SELECT statement. But the RAND function is resolved only once for the entire query, so every row will get same value. You can use an ORDER BY clause to sort the rows by the result from the NEWID function, as the following code shows: SELECT * FROM Northwind..Orders ORDER BY NEWID()
sp_who Provides information about current Microsoft® SQL Server™ users and processes. The information returned can be filtered to return only those processes that are not idle.
Have you worked on Dynamic SQL? How will You handled “ (Double Quotes) in Dynamic SQL?
How to find dependents of a table? Verify dependencies with sp_depends before dropping an object
What is the difference between a CONSTRAINT AND RULE? Rules are a backward-compatibility feature that perform some of the same functions as CHECK constraints. CHECK constraints are the preferred, standard way to restrict the values in a column. CHECK constraints are also more concise than rules; there can only be one rule applied to a column,
but multiple CHECK constraints can be applied. CHECK constraints are specified as part of the CREATE TABLE statement, while rules are created as separate objects and then bound to the column.
How to call a COM dll from SQL Server 2000? sp_OACreate – Creates an instance of the OLE object on an instance of Microsoft® SQL Server Syntax sp_OACreate progid, | clsid, objecttoken OUTPUT [ , context ] context – Specifies the execution context in which the newly created OLE object runs. If specified, this value must be one of the following: 1 = In-process (.dll) OLE server only 4 = Local (.exe) OLE server only 5 = Both in-process and local OLE server allowed
Examples
A. Use Prog ID – This example creates a SQL-DMO SQLServer object by using its ProgID.
DECLARE @object int
DECLARE @hr int
DECLARE @src varchar(255), @desc varchar(255)
EXEC @hr = sp_OACreate ‘SQLDMO.SQLServer’, @object OUT
IF @hr <> 0
BEGIN
EXEC sp_OAGetErrorInfo @object, @src OUT, @desc OUT
SELECT hr=convert(varbinary(4),@hr), Source=@src, Description=@desc
RETURN
END
B. Use CLSID – This example creates a SQL-DMO SQLServer object by using its CLSID.
DECLARE @object int
DECLARE @hr int
DECLARE @src varchar(255), @desc varchar(255)
EXEC @hr = sp_OACreate ‘{00026BA1-0000-0000-C000-000000000046}’,
@object OUT
IF @hr <> 0
BEGIN
EXEC sp_OAGetErrorInfo @object, @src OUT, @desc OUT
SELECT hr=convert(varbinary(4),@hr), Source=@src, Description=@desc
RETURN
END
Difference between sysusers and syslogins? sysusers – Contains one row for each Microsoft® Windows user, Windows group, Microsoft SQL Server™ user, or SQL Server role in the database. syslogins – Contains one row for each login account.
What is the row size in SQL Server 2000? 8060 bytes.
How will you find structure of table, all tables/views in one db, all dbs? //structure of table sp_helpdb tbl_emp //list of all databases sp_helpdb OR SELECT * FROM master.dbo.sysdatabases //details about database pubs. .mdf, .ldf file locations, size of database
sp_helpdb pubs //lists all tables under current database sp_tables OR SELECT * FROM information_schema.tables WHERE (table_type = ‘base table’) OR SELECT * FROM sysobjects WHERE type = ‘U’ //faster
B-tree indexes or doubly-linked lists?
What is the system function to get the current user’s user id? USER_ID(). Also check out other system functions like USER_NAME(), SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().
What are the series of steps that happen on execution of a query in a Query Analyzer? 1) Syntax checking 2) Parsing 3) Execution plan
Which event (Check constraints, Foreign Key, Rule, trigger, Primary key check) will be performed last for integrity check? Identity Insert Check Nullability constraint Data type check Instead of trigger Primary key Check constraint Foreign key DML Execution (update statements) After Trigger **
How will you show many to many relation in sql? Create 3rd table with 2 columns which having one to many relation to these tables.
When a query is sent to the database and an index is not being used, what type of execution is taking place? A table scan.
What is #, ##, @, @@ means? @@ – System variables @ – user defined variables
# means local temporary objects ## means global temporary objects
What is the difference between a Local temporary table and a Global temporary table? How is each one denoted? Local temporary table will be accessible to only current user session, its name will be preceded with a single hash (#mytable) Global temporary table will be accessible to all users, & it will be dropped only after ending of all active connections, its name will be preceded with double hash (##mytable)
What is covered queries in SQL Server?
Covered queries are those queries in which the columns used in where clause has proper indexes. Query uses 100% of indexes for executing it.
What is HASH JOIN, MERGE JOIN? TOOLS
Have you ever used DBCC command? Give an example for it. The Transact-SQL programming language provides DBCC statements that act as Database Console Commands for Microsoft® SQL Serve 2000. These statements check the physical and logical consistency of a database. Many DBCC statements can fix detected problems. Database Console Command statements are grouped into these categories.
Statement category
Perform
Maintenance statements
Maintenance tasks on a database, index, or filegroup.
Miscellaneous statements
Miscellaneous tasks such as enabling row-level locking or removing a dynamic-link library (DLL) from memory.
Status statements
Status checks.
Validation statements
Validation operations on a database, table, index, catalog, filegroup, system tables, or allocation of database pages.
DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc.
How do you use DBCC statements to monitor various aspects of a SQL server installation? **
What is the output of DBCC Showcontig statement? Displays fragmentation information for the data and indexes of the specified table.
How do I reset the identity column? You can use the DBCC CHECKIDENT statement, if you want to reset or reseed the identity column. For example, if you need to force the current identity value in the jobs table to a value of 100, you can use the following: USE pubs GO DBCC CHECKIDENT (jobs, RESEED, 100) GO
About SQL Command line executables
Utilities
Bcp ,console,isql,sqlagent,sqldiag,sqlmaint, sqlservr,vswitch
Dtsrun,dtswiz,isqlw,itwiz,odbccmpt,osql,rebuildm,sqlftwiz
Distrib,logread,replmerg,snapshot
scm
regxmlss
What is DTC? The Microsoft Distributed Transaction Coordinator (MS DTC) is a transaction manager that allows client applications to include several different sources of data in one transaction. MS DTC coordinates committing the distributed transaction across all the servers enlisted in the transaction.
What is DTS? Any drawbacks in using DTS? Microsoft® SQL Server™ 2000 Data Transformation Services (DTS) is a set of graphical tools and programmable objects that lets you extract, transform, and consolidate data from disparate sources into single or multiple destinations.
What is BCP? The bcp utility copies data between an instance of Microsoft® SQL Server™ 2000 and a data file in a user-specified format. C:Documents and Settingssthomas>bcp usage: bcp {dbtable | query} {in | out | queryout | format} datafile [-m maxerrors] [-f formatfile] [-e errfile] [-F firstrow] [-L lastrow] [-b batchsize] [-n native type] [-c character type] [-w wide character type] [-N keep non-text native] [-V file format version] [-q quoted identifier] [-C code page specifier] [-t field terminator] [-r row terminator] [-i inputfile] [-o outfile] [-a packetsize] [-S server name] [-U username] [-P password] [-T trusted connection] [-v version] [-R regional enable] [-k keep null values] [-E keep identity values] [-h “load hints”] How can I create a plain-text flat file from SQL Server as input to another application? One of the purposes of Extensible Markup Language (XML) is to solve challenges like this, but until all applications become XML-enabled, consider using our faithful standby, the bulk copy program (bcp) utility. This utility can do more than just dump a table; bcp also can take its input from a view instead of from a table. After you specify a view as the input source, you can limit the output to a subset of columns or to a subset of rows by selecting appropriate filtering (WHERE and HAVING) clauses. More important, by using a view, you can export data from multiple joined tables. The only thing you cannot do is specify the sequence in which the rows are written to the flat file, because a view does not let you include an ORDER BY clause in it unless you also use the TOP keyword. If you want to generate the data in a particular sequence or if you cannot predict the content of the data you want to export, be aware that in addition to a view, bcp also supports using an actual query. The only “gotcha” about using a query instead of a table or view is that you must specify queryout in place of out in the bcp command line. For example, you can use bcp to generate from the pubs database a list of authors who reside in California by writing the following code: bcp “SELECT * FROM pubs..authors WHERE state = ‘CA'” queryout c:CAauthors.txt -c -T -S
What are the different ways of moving data/databases between servers and databases in SQL Server? There are lots of options available, you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, detaching and attaching databases, replication, DTS, BCP, logshipping, INSERT…SELECT, SELECT…INTO, creating INSERT scripts to generate data.
How will I export database? Through DTS – Import/Export wizard Backup – through Complete/Differential/Transaction Log
How to export database at a particular time, every week? Backup – Schedule DTS – Schedule Jobs – create a new job
How do you load large data to the SQL server database? bcp
How do you transfer data from text file to database (other than DTS)? bcp
What is OSQL and ISQL utility? The osql utility allows you to enter Transact-SQL statements, system procedures, and script files. This utility uses ODBC to communicate with the server. The isql utility allows you to enter Transact-SQL statements, system procedures, and script files; and uses DB-Library to communicate with Microsoft® SQL Server™ 2000. All DB-Library applications, such as isql, work as SQL Server 6.5–level clients when connected to SQL Server 2000. They do not support some SQL Server 2000 features. The osql utility is based on ODBC and does support all SQL Server 2000 features. Use osql to run scripts that isql cannot run.
What Tool you have used for checking Query Optimization? What is the use of profiler in sql server? What is the first thing u look at in a SQL Profiler? SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft® SQL Server™. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures is hampering performance by executing too slowly. Use SQL Profiler to:
 Monitor the performance of an instance of SQL Server.
 Debug Transact-SQL statements and stored procedures.
 Identify slow-executing queries.
 Test SQL statements and stored procedures in the development phase of a project by single-stepping through statements to confirm that the code works as expected.
 Troubleshoot problems in SQL Server by capturing events on a production system and replaying them on a test system. This is useful for testing or debugging purposes and allows users to continue using the production system without interference.
Audit and review activity that occurred on an instance of SQL Server. This allows a security administrator to review any of the auditing events, including the success and failure of a login attempt and the success and failure of permissions in accessing statements and objects. Permissions
A user is a member of Public role and Sales role. Public role has the permission to select on all the table, and Sales role, which doesn’t have a select permission on some of the tables. Will that user be able to select from all tables?
No because the most restrictive permissions are applied
If a user does not have permission on a table, but he has permission to a view created on it, will he be able to view the data in table? Yes.
Describe Application Role and explain a scenario when you will use it?
After removing a table from database, what other related objects have to be dropped explicitly? (views and stored procedures
You have a SP names YourSP and have the a Select Stmt inside the SP. You also have a user named YourUser. What permissions you will give him for accessing the SP.
For stored procedures only execute permissions are present
Different Authentication modes in Sql server? If a user is logged under windows authentication mode, how to find his userid? There are Three Different authentication modes in sqlserver.
0. Windows Authentication Mode
1. SqlServer Authentication Mode
2. Mixed Authentication Mode
“system_user” system function in sqlserver to fetch the logged on user name.
Give the connection strings from front-end for both type logins(windows,sqlserver)? This are specifically for sqlserver not for any other RDBMS Data Source=MySQLServer;Initial Catalog=NORTHWIND;Integrated Security=SSPI (windows) Data Source=MySQLServer;Initial Catalog=NORTHWIND;Uid=” ”;Pwd=” ”(sqlserver)
What are three SQL keywords used to change or set someone’s permissions? Grant, Deny and Revoke Permissions Administration
Explain the architecture of SQL Server? **
Different types of Backups?
o A full database backup is a full copy of the database.
o A transaction log backup copies only the transaction log.
o A differential backup copies only the database pages modified after the last full database backup.
o A file or filegroup restore allows the recovery of just the portion of a database that was on the failed disk.
What are ‘jobs’ in SQL Server? How do we create one? What is tasks? Using SQL Server Agent jobs, you can automate administrative tasks and run them on a recurring basis. **
What is database replication? What are the different types of replication you can set up in SQL Server? How are they used? What is snapshot replication how is it different from Transactional replication? Replication is the process of copying/moving data between databases on the same or different servers. SQL Server supports the following types of replication scenarios:
0. Snapshot replication – It distributes data exactly as it appears at a specific moment in time and doesn’t monitor for updates. It can be used when data changes are infrequent. It is often used for browsing data such as price lists, online catalog, or data for decision support where the current data is not required and data is used as read only.
1. Transactional replication (with immediate updating subscribers, with queued updating subscribers) – With this an initial snapshot of data is applied, and whenever data modifications are made at the publisher, the individual transactions are captured and propagated to the subscribers.
2. Merge replication – It is the process of distributing the data between publisher and subscriber, it allows the publisher and subscriber to update the data while connected or disconnected, and then merging the updates between the sites when they are connected.
How can u look at what are the process running on SQL server? How can you kill a process in SQL server?
o Expand a server group, and then expand a server.
o Expand Management, and then expand Current Activity.
o Click Process Info. The current server activity is displayed in the details pane.
In the details pane, right-click a Process ID, and then click Kill Process.
What is RAID and what are different types of RAID configurations? RAID stands for Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. There are six RAID levels 0 through 5 offering different levels of performance, fault tolerance.
Some of the tools/ways that help you troubleshooting performance problems are:
SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer.
How to determine the service pack currently installed on SQL Server? The global variable @@Version stores the build number of the sqlservr.exe, which is used to determine the service pack installed. eg: Microsoft SQL Server 2000 – 8.00.760 (Intel X86) Dec 17 2002 14:22:05 Copyright (c) 1988-2003 Microsoft Corporation Enterprise Edition on Windows NT 5.0 (Build 2195: Service Pack 3)
What is the purpose of using COLLATE in a query? The term, collation, refers to a set of rules that determine how data is sorted and compared. In Microsoft® SQL Server 2000, it is not required to separately specify code page and sort order for character data, and the collation used for Unicode data. Instead, specify the collation name and sorting rules to use. Character data is sorted using rules that define the correct character sequence, with options for specifying case-sensitivity, accent marks, kana character types, and character width. Microsoft SQL Server 2000 collations include these groupings:
 Windows collations – Windows collations define rules for storing character data based on the rules defined for an associated Windows locale. The base Windows collation rules specify which alphabet or language is used when dictionary sorting is applied, as well as the code page used to store non-Unicode character data. For Windows collations, the nchar, nvarchar, and ntext data types have the same sorting behavior as char, varchar, and text data types
 SQL collations – SQL collations are provided for compatibility with sort orders in earlier versions of Microsoft SQL Server.
Sort Order Binary is the fastest sorting order, and is case-sensitive. If Binary is selected, the Case-sensitive, Accent-sensitive, Kana-sensitive, and Width-sensitive options are not available.
Sort order
Description
Binary
Sorts and compares data in Microsoft® SQL Server™ tables based on the bit patterns defined for each character. Binary sort order is case-sensitive, that is lowercase precedes uppercase, and accent-sensitive. This is the fastest sorting order. If this option is not selected, SQL Server follows sorting and comparison rules as defined in dictionaries for the associated language or alphabet.
Case-sensitive
Specifies that SQL Server distinguish between uppercase and lowercase letters. If not selected, SQL Server considers the uppercase and lowercase versions of letters to be equal. SQL Server does not define whether lowercase letters sort lower or higher in relation to uppercase letters when Case-sensitive is not selected.
Accent-sensitive
Specifies that SQL Server distinguish between accented and unaccented characters. For example, ‘a’ is not equal to ‘á’. If not selected, SQL Server considers the accented and unaccented versions of letters to be equal.
Kana-sensitive
Specifies that SQL Server distinguish between the two types of Japanese kana characters: Hiragana and Katakana. If not selected, SQL Server considers Hiragana and Katakana characters to be equal.
Width-sensitive
Specifies that SQL Server distinguish between a single-byte character (half-width) and the same character when represented as a double-byte character (full-width). If not selected, SQL Server considers the single-byte and double-byte representation of the same character to be equal.
Windows collation options:
 Use Latin1_General for the U.S. English character set (code page 1252).
 Use Modern_Spanish for all variations of Spanish, which also use the same character set as U.S. English (code page 1252).
 Use Arabic for all variations of Arabic, which use the Arabic character set (code page 1256).
 Use Japanese_Unicode for the Unicode version of Japanese (code page 932), which has a different sort order from Japanese, but the same code page (932).
What is the STUFF Function and how does it differ from the REPLACE function? STUFF – Deletes a specified length of characters and inserts another set of characters at a specified starting point. SELECT STUFF(‘abcdef’, 2, 3, ‘ijklmn’) GO Here is the result set: ——— aijklmnef
REPLACE – Replaces all occurrences of the second given string expression in the first string expression with a third expression. SELECT REPLACE(‘abcdefghicde’,’cde’,’xxx’) GO Here is the result set:
———— abxxxfghixxx
What does it mean to have quoted_identifier on? What are the implications of having it off? When SET QUOTED_IDENTIFIER is OFF (default), literal strings in expressions can be delimited by single or double quotation marks. When SET QUOTED_IDENTIFIER is ON, all strings delimited by double quotation marks are interpreted as object identifiers. Therefore, quoted identifiers do not have to follow the Transact-SQL rules for identifiers. SET QUOTED_IDENTIFIER must be ON when creating or manipulating indexes on computed columns or indexed views. If SET QUOTED_IDENTIFIER is OFF, CREATE, UPDATE, INSERT, and DELETE statements on tables with indexes on computed columns or indexed views will fail. The SQL Server ODBC driver and Microsoft OLE DB Provider for SQL Server automatically set QUOTED_IDENTIFIER to ON when connecting. When a stored procedure is created, the SET QUOTED_IDENTIFIER and SET ANSI_NULLS settings are captured and used for subsequent invocations of that stored procedure. When executed inside a stored procedure, the setting of SET QUOTED_IDENTIFIER is not changed. SET QUOTED_IDENTIFIER OFF GO — Attempt to create a table with a reserved keyword as a name — should fail. CREATE TABLE “select” (“identity” int IDENTITY, “order” int) GO SET QUOTED_IDENTIFIER ON GO — Will succeed. CREATE TABLE “select” (“identity” int IDENTITY, “order” int) GO
What is the purpose of UPDATE STATISTICS? Updates information about the distribution of key values for one or more statistics groups (collections) in the specified table or indexed view.
What do u mean by OLAP server? What is the difference between OLAP and OLTP?
What is a tuple? A tuple is an instance of data within a relational database.
sp_configure commands? Displays or changes global configuration settings for the current server.
What is the basic functions for master, msdb, tempdb databases? Microsoft® SQL Server 2000 systems have four system databases:
 master – The master database records all of the system level information for a SQL Server system. It records all login accounts and all system configuration settings. master is the database that records the existence of all other databases, including the location of the database files.
 tempdb – tempdb holds all temporary tables and temporary stored procedures. It also fills any other temporary storage needs such as work tables generated by SQL Server. tempdb is re-created every time SQL Server is started so the system starts with a clean copy of the database. By default, tempdb autogrows as needed while SQL Server is running. If the size defined for tempdb is small, part of your system processing load may be taken up with autogrowing tempdb to the size needed to support your workload each time to restart SQL Server. You can avoid this overhead by using ALTER DATABASE to increase the size of tempdb.
 model – The model database is used as the template for all databases created on a system. When a CREATE DATABASE statement is issued, the first part of the database is created by copying in the contents of the model database, then the remainder of the new database is filled with empty pages. Because tempdb is created every time SQL Server is started, the model database must always exist on a SQL Server system.
 msdb – The msdb database is used by SQL Server Agent for scheduling alerts and jobs, and recording operators.
What are sequence diagrams? What you will get out of this sequence diagrams? Sequence diagrams document the interactions between classes to achieve a result, such as a use case. Because UML is designed for object-oriented programming, these communications between classes are known as messages. The sequence diagram lists objects horizontally, and time vertically, and models these messages over time.
What are the new features of SQL 2000 than SQL 7? What are the new datatypes in sql?
 XML Support – The relational database engine can return data as Extensible Markup Language (XML) documents. Additionally, XML can also be used to insert, update, and delete values in the database. (for xml raw – to retrieve output as xml type)
 User-Defined Functions – The programmability of Transact-SQL can be extended by creating your own Transact-SQL functions. A user-defined function can return either a scalar value or a table.
 Indexed Views – Indexed views can significantly improve the performance of an application where queries frequently perform certain joins or aggregations. An indexed view allows indexes to be created on views, where the result set of the view is stored and indexed in the database.
 New Data Types – SQL Server 2000 introduces three new data types. bigint is an 8-byte integer type. sql_variant is a type that allows the storage of data values of different data types. table is a type that allows applications to store results temporarily for later use. It is supported for variables, and as the return type for user-defined functions.
 INSTEAD OF and AFTER Triggers – INSTEAD OF triggers are executed instead of the triggering action (for example, INSERT, UPDATE, DELETE). They can also be defined on views, in which case they greatly extend the types of updates a view can support. AFTER triggers fire after the triggering action. SQL Server 2000 introduces the ability to specify which AFTER triggers fire first and last.
 Multiple Instances of SQL Server – SQL Server 2000 supports running multiple instances of the relational database engine on the same computer. Each computer can run one instance of the relational database engine from SQL Server version 6.5 or 7.0, along with one or more instances of the database engine from SQL Server 2000. Each instance has its own set of system and user databases.
 Index Enhancements – You can now create indexes on computed columns. You can specify whether indexes are built in ascending or descending order, and if the database engine should use parallel scanning and sorting during index creation.
How do we open SQL Server in single user mode? We can accomplish this in any of the three ways given below :-
. From Command Prompt :- sqlservr -m
a. From Startup Options :- Go to SQL Server Properties by right-clicking on the Server name in the Enterprise manager. Under the ‘General’ tab, click on ‘Startup Parameters’. Enter a value of -m in the Parameter.
b. From Registry :- Go to HKEY_LOCAL_MACHINESoftwareMicrosoftMSSQLServerMSSQLServerParam
eters. Add new string value. Specify the ‘Name’ as SQLArg(n) & ‘Data’ as -m. Where n is the argument number in the list of arguments.
What is Log Shipping? In Microsoft® SQL Server™ 2000 Enterprise Edition, you can use log shipping to feed transaction logs from one database to another on a constant basis. Continually backing up the transaction logs from a source database and then copying and restoring the logs to a destination database keeps the destination database synchronized with the source database. This allows you to have a backup server and also provides a way to offload query processing from the main computer (the source server) to read-only destination servers.
XML
How can I convert data in a Microsoft Access table into XML format? The following applications can help you convert Access data into XML format: Access 2002, ADO 2.5, and SQLXML. Access 2002 (part of Microsoft Office XP) enables you to query or save a table in XML format. You might be able to automate this process. ADO 2.5 and later enables you to open the data into a recordset, then persist the recordset in XML format, as the following code shows: rs.Save “c:rs.xml”, adPersistXML You can use linked servers to add the Access database to your SQL Server 2000 database so you can run queries from within SQL Server to retrieve data. Then, through HTTP, you can use the SQLXML technology to extract the Access data in the XML format you want. NEW
@@IDENTITY ? Ans: Returns the last-inserted identity value.
How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?
One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships. One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships. Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table. It will be a good idea to read up a database designing fundamentals text book. What’s the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only. What are user defined datatypes and when you should go for them?
User defined datatypes let you extend the base SQL Server datatypes by providing a descriptive name, and format to the database. Take for example, in your database, there is a column called Flight_Num which appears in many tables. In all these tables it should be varchar(8). In this case you could create a user defined datatype called Flight_num_type of varchar(8) and use it across all your tables. See sp_addtype, sp_droptype in books online. What is bit datatype and what’s the information that can be stored inside a bit column?
Bit datatype is used to store boolean information like 1 or 0 (true or false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0 and there was no support for NULL. But from SQL Server 7.0 onwards, bit datatype can represent a third state, which is NULL.
Define candidate key, alternate key, composite key.
A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys. A key formed by combining at least two or more columns is called composite key. What are defaults? Is there a column to which a default can’t be bound?
A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can’t have defaults bound to them. See CREATE DEFUALT in books online. CREATE INDEX myIndex ON myTable(myColumn) What type of Index will get created after executing the above statement?
Non-clustered index. Important thing to note: By default a clustered index gets created on the primary key, unless specified otherwise. Explain Active/Active and Active/Passive cluster configurations
Hopefully you have experience setting up cluster servers. But if you don’t, at least be familiar with the way clustering works and the two clustering configurations Active/Active and Active/Passive. SQL Server books online has enough information on this topic and there is a good white paper available on Microsoft site. What’s the difference between DELETE TABLE and TRUNCATE TABLE commands?
TRUNCATE TABLE is functionally identical to DELETE statement with no WHERE clause: both remove all rows in the table. But TRUNCATE TABLE is faster and uses fewer system and transaction log resources than DELETE.
The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log.
TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. The counter used by an identity for new rows is reset to the seed for the column. If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.
You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint; instead, use DELETE statement without a WHERE clause. Because TRUNCATE TABLE is not logged, it cannot activate a trigger. .Explain the storage models of OLAP
Check out MOLAP, ROLAP and HOLAP in SQL Server books online for more information. What are constraints? Explain different types of constraints.
Constraints enable the RDBMS enforce the integrity of the database automatically, without needing you to create triggers rule or defaults. Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY For an explanation of these constraints see books online for the pages titled: “Constraints” and “CREATE TABLE”, “ALTER TABLE” What is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. what are the advantages and disadvantages of this approach?
Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quicker. Indexes are of two types. Clustered indexes and non-clustered indexes. When you create a clustered index on a table, all the rows in the table are stored in the order of the clustered index key. So, there can be only one clustered index per table. Non-clustered indexes have their own storage separate from the table data storage. Non-clustered indexes are stored as B-tree structures (so do clustered indexes), with the leaf level nodes having the index key and it’s row locater. The row located could be the RID or the Clustered index key, depending up on the absence or presence of clustered index on the table. If you create an index on each column of a table, it improves the query performance, as the query optimizer can choose from all the existing indexes to come up with an efficient execution plan. At the same t ime, data modification operations (such as INSERT, UPDATE, DELETE) will become slow, as every time data changes in the table, all the indexes need to be updated. Another disadvantage is that, indexes need disk space, the more indexes you have, more disk space is used.
RAID stands for Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. There are six RAID levels 0 through 5 offering different levels of performance, fault tolerance. MSDN has some information about RAID levels and for detailed information, check out the RAID advisory board’s homepage What are the steps you will take to improve performance of a poor performing query?
This is a very open ended question and there could be a lot of reasons behind the poor performance of a query. But some general issues that you could talk about would be: No indexes, table scans, missing or out of date statistics, blocking, excess recompilations of stored procedures, procedures and triggers without SET NOCOUNT ON, poorly written query with unnecessarily complicated joins, too much normalization, excess usage of cursors and temporary tables. Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer. Download the white paper on performance tuning SQL Server from Microsoft web site. Don’t forget to check out sql-server-performance.com What are the steps you will take, if you are tasked with securing an SQL Server?
Again this is another open ended question. Here are some things you could talk about: Preferring NT authentication, using server, databse and application roles to control access to the data, securing the physical database files using NTFS permissions, using an unguessable SA password, restricting physical access to the SQL Server, renaming the Administrator account on the SQL Server computer, disabling the Guest account, enabling auditing, using multiprotocol encryption, setting up SSL, setting up firewalls, isolating SQL Server from the web server etc. Read the white paper on SQL Server security from Microsoft website. Also check out My SQL Server security best practices What is blocking and how would you troubleshoot it?
Blocking happens when one connection from an application holds a lock and a second connection requires a conflicting lock type. This forces the second connection to wait, blocked on the first. Read up the following topics in SQL Server books online: Understanding and avoiding blocking, Coding efficient transactions. Explain CREATE DATABASE syntax
Many of us are used to creating databases from the Enterprise Manager or by just issuing the command: CREATE DATABAE MyDB. But what if you have to create a database with two filegroups, one on drive C and the other on drive D with log on drive E with an initial size of 600 MB and with a What is RAID and what are different types of RAID configurations?
growth factor of 15%? That’s why being a DBA you should be familiar with the CREATE DATABASE syntax. Check out SQL Server books online for more information. How to restart SQL Server in single user mode? How to start SQL Server in minimal configuration mode?
SQL Server can be started from command line, using the SQLSERVR.EXE. This EXE has some very important parameters with which a DBA should be familiar. -m is used for starting SQL Server in single user mode and -f is used to start the SQL Server in minimal configuration mode. Check out SQL Server books online for more parameters and their explanations. As a part of your job, what are the DBCC commands that you commonly use for database maintenance?
DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc. But there are a whole load of DBCC commands which are very useful for DBAs. Check out SQL Server books online for more information.
What are statistics, under what circumstances they go out of date, how do you update them?
Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query.
Some situations under which you should update statistics: 1) If there is significant change in the key values in the index 2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated 3) Database is upgraded from a previous version Look up SQL Server books online for the following commands: UPDATE STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS, CREATE STATISTICS, DROP STATISTICS, sp_autostats, sp_createstats, sp_updatestats What are the different ways of moving data/databases between servers and databases in SQL Server?
There are lots of options available, you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, dettaching and attaching databases, replication, DTS, BCP, log shipping, INSERT…SELECT, SELECT…INTO, creating INSERT scripts to generate data. Explian different types of BACKUPs avaialabe in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?
Types of backups you can create in SQL Sever 7.0+ are Full database backup, differential database backup, transaction log backup, filegroup backup. Check out the BACKUP and RESTORE commands in SQL Server books online. Be prepared to write the commands in your . Books online also has information on detailed backup/restore architecture and when one should go for a particular kind of backup.
Write down the general syntax for SELECT statements covering all the options.
Here’s the basic syntax: (Also checkout SELECT in books online for advanced syntax). SELECT select_list [INTO new_table_] FROM table_source [WHERE search_condition] [GROUP BY group_by_expression] [HAVING search_condition] [ORDER BY order_expression [ASC | DESC] ] Can you have a nested transaction?
Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and @@TRANCOUNT What are triggers? How many triggers you can have on a table? How to invoke a trigger on demand?
Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table. In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there’s no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder Triggers can’t be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, DELETE) happens on the table on which they are defined. Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster. Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also. Search SQL Server 2000 books online for INSTEAD OF triggers. Also check out books online for ‘inserted table’, ‘deleted table’ and COLUMNS_UPDATED () There is a trigger defined for INSERT operations on a table, in an OLTP system. The trigger is written to instantiate a COM object and pass the newly inserted rows to it for some custom processing. What do you think of this implementation? Can this be implemented better?
Instantiating COM objects is a time consuming process and since you are doing it from within a trigger, it slows down the data insertion process. Same is the case with sending emails from triggers. This scenario can be better implemented by logging all the necessary data into a separate table, and have a job, which periodically checks this table and does the needful. What is a self-join? Explain it with an example.
Self join is just like any other join, except that two instances of the same table will be joined in the query. Here is an example: Employees table which contains rows for normal employees as well as managers. So, to find out the managers of all the employees, you need a self join. CREATE TABLE emp ( empid int, mgrid int, empname char(10) ) INSERT emp SELECT 1,2,’Vyas’ INSERT emp SELECT 2,3,’Mohan’ INSERT emp SELECT 3,NULL,’Shobha’ INSERT emp SELECT 4,2,’Shridhar’ INSERT emp SELECT 5,2,’Sourabh’ SELECT t1.empname [Employee], t2.empname [Manager] FROM emp t1, emp t2 WHERE t1.mgrid = t2.empid
Here’s an advanced query using a LEFT OUTER JOIN that even returns the employees without managers (super bosses) SELECT t1.empname [Employee], COALESCE(t2.empname, ‘No manager’) [Manager] FROM emp t1 LEFT OUTER JOIN emp t2 ON t1.mgrid = t2.empid Given an employee table, how would you find out the second highest salary?
For a solution see the ‘My code library’ section of this site.
SQL Server FAQ 2 Why are my insert, update statements failing with the following error? Server: Msg 8152, Level 16, State 9, Line 1 String or binary data would be truncated. The statement has been terminated. <top>
This error occurs, when the length of the value entered by you into a char, varchar, nchar, nvarchar column is longer than the maximum length of the column. For example, inserting ‘FAQ’ into a char(2) column would result in this error. Profiler is handy in troubleshooting this error. If data truncation is okay with you and you don’t want to see this error, then turn off ANSI WARNINGS by using the following SET command: SET ANSI_WARNINGS OFF. Steps to reproduce the problem: CREATE TABLE MyTable ( Pkey int PRIMARY KEY, Col1 char(10) ) GO INSERT INTO MyTable (Pkey, Col1) VALUES (1, ‘SQL Server Clustering FAQ’) GO Make sure, you restrict the length of input, in your front-end applications. For example, you could use the MAXLENGTH property of the text boxes in HTML forms. E.g: <INPUT NAME = “Name” TYPE= TEXTBOX MAXLENGTH=20> What is the T-SQL equivalent of IIF (immediate if/ternary operator) function of other programming languages? <top>
CASE is the equivalent of IIF function. See SQL Server Books Online for more information. Here’s a quick example: CREATE TABLE People ( [ID] int PRIMARY KEY, [Name] varchar(25) NOT NULL, Sex bit NULL ) INSERT INTO People ([ID],[Name], Sex) VALUES (1,’John Dykes’, 1) INSERT INTO People ([ID],[Name], Sex) VALUES (2,’Deborah Crook’, 0) INSERT INTO People ([ID],[Name], Sex) VALUES (3,’P S Subramanyam’, NULL) SELECT [ID], [Name], CASE Sex WHEN 1 THEN ‘Male’ WHEN 0 THEN ‘Female’ ELSE ‘Not specified’ END AS Sex FROM People How to programmatically find out when the SQL Server service started?
Everytime SQL Server starts, it recreates the tempdb database. So, the creation date and time of the tempdb database tells us the date and time at which SQL Server service started. This information is stored in the crdate column of the sysdatabases table in master database. Here’s the query to find that out: SELECT crdate AS ‘SQL Server service started approximately at:’ FROM master.dbo.sysdatabases
WHERE name = ‘tempdb’ SQL Server error log also has this information (This is more accurate) and the error log can be queried using xp_readerrorlog How to get rid of the time part from the date returned by GETDATE function?
We have to use the CONVERT function to strip the time off the date. Any of the following commands will do this: SELECT CONVERT(char,GETDATE(),101) SELECT CONVERT(char,GETDATE(),102) SELECT CONVERT(char,GETDATE(),103) SELECT CONVERT(char,GETDATE(),1) See SQL Server Books Online for more information on CONVERT function. How to upload images or binary files into SQL Server tables? <top>
First of all, if possible, try not to stored images and other binary files in the SQL Server tables, as they slow things down. Instead, store a link (file path) to the file in the tables and let your applications directly access the files. But if you must store these files within SQL Server, use the text/ntext or image datatype columns and consider the following options:
 SQL Server 7.0 and 2000 come with a utility called textcopy.exe. You can locate this file in the Binn folder under your SQL Server installation folder. Run this file from command prompt, and it will prompt you for required input
 Use the GetChunk and AppendChunk methods of ADO Field object. MSDN has examples
 Use the ADO Stream object
 Use the Bulk Insert Image utility (BII) that ships with SQL Server 2000 (Can be found at Program FilesMicrosoft SQL Server80ToolsDevtoolsSamplesUtils) How to run an SQL script file that is located on the disk, using T-SQL? <top>
There’s no direct command to read a script file and execute it. But the isql.exe and osql.exe come in handy when you have to execute a script file from within T-SQL. Just call any of these exes using xp_cmdshell and pass the script file name as parameter to it. See SQL Server Books Online for more information about the input parameters of these exes. Here are some quick examples: EXEC master..xp_cmdshell ‘osql -Svaio -Usa -Pzaassds1 -ic:MySQl.sql -n’ EXEC master..xp_cmdshell ‘isql -Svaio -Usa -Pzaassds1 -ic:MySQl.sql -n’ See xp_cmdshell in SQL Server Books Online if you are having permissions problems in getting this technique to work. How to get the complete error message from T-SQL while error handling? <top>
Unfortunately, the error handling capabilities of SQL Server are limited. When an error occurs, all you can get is the error number, using the @@ERROR global variable. There is no @@ERROR_MESSAGE global variable to get the error description. For a complete error message, you can always query the master..sysmessages table using the error number, but most of these messages have place holders (like %s, %l etc.), and hence we can’t get the complete error message. However, the client applications using an object model such as RDO, ADO have access to the complete error message. How to get the first day of the week, last day of the week and last day of the month using T-SQL date functions? <top>
Here’s the code: DECLARE @Date datetime SET @Date = ‘2001/08/31’ SELECT DATEADD(dd,-(DATEPART(dw, @Date) – 1),@Date) AS ‘First day of the week’ SELECT DATEADD(dd,-(DATEPART(dw, @Date) – 7),@Date) AS ‘Last day of the week’ SELECT DAY(DATEADD(d, -DAY(DATEADD(m,1,@Date)),DATEADD(m,1,@Date))) AS ‘Last day of the month’
How to pass a table name, column name etc. to the stored procedure so that I can dynamically select from a table
Basically, SELECT and other commands like DROP TABLE won’t let you use a variable instead of a hardcoded table name. To overcome this problem, you have to use dynamic sql. But dynamic SQL has some disadvantages. It’s slow, as the dynamic SQL statement needs to be parsed everytime it’s executed. Further, the user who is executing the dynamic SQL string needs direct permissions on the tables, which defeats the purpose of having stored procedures to mask the underlying tables. Having said that, here are some examples of dynamic SQL: (Also see sp_executesql in SQL Server Books Online) CREATE PROC DropTable @Table sysname AS EXEC (‘DROP TABLE ‘ + @Table) GO EXEC DropTable ‘MyTable’ GO CREATE PROC SelectTable @Table sysname AS EXEC (‘SELECT * FROM ‘ + @Table) GO EXEC SelectTable ‘MyTable’ For a complete discussion on the pros and cons of dynamic SQL check out Erland’s article: The curse and blessings of dynamic SQL Error inside a stored procedure is not being raised to my front-end applications using ADO. But I get the error when I run the procedure from Query Analyzer
This typically happens when your stored procedure is returning multiple resultsets and the offending SQL statement is executed after returning one or more resultsets. ADO will not return an error untill it processes all the recordsets returned before the offending SQL statement got executed. So, to get to the error message returned by your procedure. You have to loop through all the recordsets returned. ADO Recordset object has a method called NextRecordset, which lets you loop through the recordsets. Having SET NOCOUNT ON at the beginning of the procedure also helps avoid this problem. SET NOCOUNT ON also helps in improving the stored procedure performance. Here’s a sample procedure to simulate the problem: CREATE PROC TestProc AS SELECT MAX(Col1) FROM TestTable SELECT MIN(Col1) FROM TestTable INSERT INTO TestTable (Col1, Col2) VALUES (1,’Oracle and SQL Server comparison’) INSERT INTO TestTable (Col1, Col2) VALUES (1,’How to configure SQL Server?’) — Dupplicate key error occurs GO How to suppress error messages in stored procedures/triggers etc. using T-SQL?
It’s not possible to suppress error messages from within T-SQL. Error messages are always returned to the client. If you don’t want your users to see these raw error messages, you should handle them in your front-end applications. For example, if you are using ADO from ASP to connect to SQL Server, you would do something like the following:
On Error Resume Next Set Rs = Conn.Execute (“INSERT INTO MyTable (1,’How to migrate from Oracle to SQL Server’,’Book'”) If Err.Number <> 0 Then Response.Write (“Error occurred while inserting new data”) On Error GoTo 0 How to save the output of a query/stored procedure to a text file using T-SQL?
T-SQL by itself has no support for saving the output of queries/stored procedures to text files. But you could achieve this using the command line utilities like isql.exe and osql.exe. You could either invoke these exe files directly from command prompt/batch files or from T-SQL using the xp_cmdshell command. Here are the examples: From command prompt: osql.exe -S YourServerName -U sa -P secretcode -Q “EXEC sp_who2” -o “E:output.txt” From T-SQL: EXEC master..xp_cmdshell ‘osql.exe -S YourServerName -U sa -P secretcode -Q “EXEC sp_who2” -o “E:output.txt”‘ Query Analyzer lets you save the query output to text files manually. The output of stored procedures that are run as a part of a scheduled job, can also be saved to a text file. BCP and Data Transformation Services (DTS) let you export table data to text files. How to join tables from different databases? <top>
You just have to qualify the table names in your SELECT queries with database name, followed by table owner name. In the following example, Table1 from pubs database and Table2 from northwind database are being joined on the column i. Both tables are owned by dbo. SELECT a.i, a.j FROM pubs.dbo.Table1 a INNER JOIN northwind.dbo.Table2 b ON a.i = b.i GO How to join tables from different servers? <top>
To be able to join tables between two SQL Servers, first you have to link them. After the linked servers are setup, you just have to prefix your tables names with server name, database name, table owner name in your SELECT queries. The following example links SERVER_01 to SERVER_02. Execute the following commands in SERVER_02: EXEC sp_addlinkedserver SERVER_01 GO /* The following command links ‘sa’ login on SERVER_02 with the ‘sa’ login of SERVER_01 */ EXEC sp_addlinkedsrvlogin @rmtsrvname = ‘SERVER_01’, @useself = ‘false’, @locallogin = ‘sa’, @rmtuser = ‘sa’, @rmtpassword = ‘sa password of SERVER_01’ GO SELECT a.title_id FROM SERVER_01.pubs.dbo.titles a INNER JOIN SERVER_02.pubs.dbo.titles b ON a.title_id = b.title_id GO How to convert timestamp data to date data (datetime datatype)? <top>
The name timestamp is a little misleading. Timestamp data has nothing to do with dates and times and can not be converted to date data. A timestamp is a unique number within the database and is equivalent to a binary(8)/varbinary(8) datatype. A table can have only one timestamp column.
Timestamp value of a row changes with every update of the row. To avoid the confusion, SQL Server 2000 introduced a synonym to timestamp, called rowversion. Can I invoke/instantiate COM objects from within stored procedures or triggers using T-SQL?
Yes. SQL Server provides system stored procedures that let you instantiate COM objects using T-SQL from stored procedures, triggers and SQL batches. Search SQL Server Books Online for sp_OACreate and sp_OA* for documentation and examples. Also check out my code library for an example. Oracle has a rownum to access rows of a table using row number or row id. Is there any equivalent for that in SQL Server? Or how to generate output with row number in SQL Server?
There is no direct equivalent to Oracle’s rownum or row id in SQL Server. Strictly speaking, in a relational database, rows within a table are not ordered and a row id won’t really make sense. But if you need that functionality, consider the following three alternatives:
 Add an IDENTITY column to your table. See Books Online for more information
 Use the following query to generate a row number for each row. The following query generates a row number for each row in the authors table of pubs database. For this query to work, the table must have a unique key. SELECT (SELECT COUNT(i.au_id) FROM pubs..authors i WHERE i.au_id >= o.au_id ) AS RowID, au_fname + ‘ ‘ + au_lname AS ‘Author name’ FROM pubs..authors o ORDER BY RowID
 Use a temporary table approach, to store the entire resultset into a temporary table, along with a row id generated by the IDENTITY() function. Creating a temporary table will be costly, especially when you are working with large tables. Go for this approach, if you don’t have a unique key in your table. Search for IDENTITY (Function) in SQL Server Books Online.
For more ideas on this topic, click here to read an informative article from Microsoft Knowledgebase. How to specify a network library like TCP/IP using ADO connect string?
To specify TCP/IP net library, append the following to your ADO connect string: Network=dbmssocn For more information on specifying other net libraries in ADO connect strings, click here to read the article from Microsoft Knowledgebase. Is there a way to find out when a stored procedure was last updated? <top>
Simple answer is ‘No’. The crdate column in the sysobjects table always contains the stored procedure create date, not the last updated date. You can use Profiler to trace ALTER PROC calls to the database, but you can’t really afford to run a trace for ever, as it’s resource intensive. Here is a simple idea! Whenever you have to alter your stored procedure, first drop it, then recreate it with the updated code. This resets the crdate column of sysobjects table. If you can make sure your developers always follow this plan, then the crdate column of sysobjects will always reflect the last updated date of the stored procedure. For example, if I have to modify a procedure named MyProc, instead of doing “ALTER PROC MyProc”, here’s what I would do: – Use sp_helptext to get the current code of MyProc. – Change the code as needed. – Run the following code to drop the existing version of MyProc: IF EXISTS(SELECT 1 FROM sysobjects WHERE name = ‘MyProc’ AND type = ‘P’ AND USER_NAME(uid) = ‘dbo’) BEGIN DROP PROC dbo.MyProc END – Run the updated code to recreate MyProc
Visual Source Safe Information There is a much more powerful way out, if you can use Visual Source Safe (VSS). VSS is a version
control software, that lets you manage your code. With VSS in place, you will have to maintain all your object creation scripts as script files and check them into VSS. When you have to modify a particular stored procedure, check out that script from VSS, modify it, test it, create the stored procedure, and check the script back into VSS. VSS can show you when a script got modified, by who and a whole lot of other information. Advantages of using VSS – You can version control your software, as VSS maintains all your changes as different versions – You can go back to a previous known good version of your stored procedure, if a developer makes a mistake – Using the labelling feature, you can revert back to an entire set of scripts at a particular point in time – You can control access to your source code by configuring permissions to your developers – By maintaining backups of VSS database, you can secure all your code centrally, instead of worrying about individual script files
Given an employee table, how would you find out the second highest salary?
SELECT MIN(Salary) FROM ( SELECT TOP 2 Salary FROM Employees ORDER BY Salary Desc ) AS A
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Incremental Load Using Talend

overallDesc
Hi Readers,
                  Incremental Load is way of loading your target tables in data warehouse such that new or updated data from your source system will only affect your target system. 
It’s pretty similar with your novel reading, let’s say first day you read some pages then on other day you will start reading from the point you left and so on.
So, today we will discuss one of the implementation technique for incremental loading using Talend Open Studio.

Overall Job Desc:-

overall_structure

Execution Steps:

1. Create two context variables one will hold the directory structure of your parameter file(file will store your last run date info) specify some default value which you can further change using property file while deployment and the other variable is used within the job to hold the last run status. Load the last run context variable using tContextLoad.
2. Create a sql query which will hit your source database and pull down data as per your needs. In my case   query is with condition tdate < sysdate and tdate>'”+context.Last_Load_Date+”‘”.
As in most of the cases reporting is done till the previous day data, tdate is a column which holds the record’s updated/insert date status so we are pulling data as per the given condition. 
Total Data Fetched = Data Greater than Last_Time_Run + Data Less then current_date.  
3.Simple update your parameter file that is holding your previous run date with current_date-1.
“select ‘Last_Load_Date;’||to_char(sysdate-1,’dd-mon-yyyy’) as prev_day from dual”









Thanks for reading..:)  

Talend Interview Questions                                                               

Author: Ankit Kansal & Nayan Naik
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Dynamic Column Ordering From Source File In Informatica

source_struc
Hello Readers,
                      Today we will be discussing a scenario which commonly occurs during ETL development. Lets say we have a source file which contains  Employee information as described in the following given text file.
source_info
SCENARIO:- The given source file will be available to you on daily basis, but the order of the given columns varies daily  such that the ordering of the columns doesn’t remain constant . Today we have ename in first position ,the next day it may appear in the last position. Hence you cannot implement the logic straight away as we know that you must know your column ordering in informatica to implement the further logic.
So, to overcome this current situation we have developed a mapping which will provide you a sure shot solution and you can re modify this mapping as per your business needs.
COMPLETE JOB DESC:-

overall_job_desc

SOLUTION:-

Take the number of mapping variable as per number of columns in your source file. In my case i have three columns so i have defined three variables of Integer data type named as $$var1,$$var2,$$var3 set initial value to 0 while defining them.
Actual Implementation will be done in Expression Transformation. 
So carefully look into the given snapshot for expression transformation.
Now in expression transformation create four expr_variables as defined they were used for setting up the values of mapping variables. var_count is used for setting up the values first time for all the mapping variables.
now for var_ename variable use the code given below.
The code given above will check for the first time whether count is one(ie the header row) if yes then it checks if the column name ename for the  first row and if  contains data as ‘ename’ then setvariable($$var1,1) similarly it checks all columns for data ‘ename’ and sets the any of $var which satisfies the condition. 
Same code is repeated all the times for all column names but only the difference is the checking condition. Like deptno it will check whether the columns contains ‘deptno’ and if yes then it sets setvariable($$var1,2)and so on.
*remember to pull the data from the first row of the file don’t ignore the first like otherwise it will not work however you can skip your first row after you recognized your columns using filter in the next component.

Now Finally create three output ports which will be used to forward your corrected data to your next transformation. So again look into the code given below.
Similarly, use similar condition in all your output ports like for ename use $$var1 any of the variable holding your ename data will be satisfied here similarly you can define for rest of your ports. Further on condition will change just a bit instead of $$var1=1 use have to use $$var1=2 or 3 whatever you have specified before.
O/P:-



Thank u for reading…


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Date Dimension Using Talend

first
Hello Readers,
                      In our previous post we discussed what is the use of Date Time Dimension in Warehousing environment and shown a demo displaying a Date-Time Dimension using Informatica.

So, in this post we will demonstrate the same implementation using Talend Open Studio.

COMPONENTS TAKEN:-

1)Oracle Db(tOracleConnection)
2)tMap(for data manipulation)
3)tConvertType(to change the data type)
4)tLogRow(Displaying Result)

COMPLETE JOB DESCRIPTION:-

job_info

Now,
         In tOracleInput component define two columns as a schema both must be of data type and in sql editor write the query given below.

“select sysdate+level,trunc(sysdate+level,’q’) from dual connect by level < 366”

first column will return you data serially from the current date and second column will give you first date for every quarter.

Most of the implementation is completed using existing  components.
To compute monthOfQuarter–
var monthOfQuarter=Mathematical.MOD(TalendDate.getPartOfDate(“MONTH”,row1.ora_date)+1,3)  
then
(Var.monthOfQuarter==0.0)?3.0:Var.monthOfQuarter 

To pull out Weekday in character format use–
TalendDate.formatDate(“EEEE”,row1.ora_date)

To calculate days from first date of quarter–
TalendDate.diffDate(row1.ora_date,Var.quaterFirstDate,”DD”)+1    


So, this is how you can implement a basic date-time dimension. Beyond this you can alter this current implementation as per your requirement.

Thanks for giving your precious time….kindly leave a comment  in case of any queries ..

Talend Interview Questions

Author : Ankit Kansal & Nayan Naik

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Date Dimension Using Informatica

Complete
Hello Readers,
                       Today we will be discussing one of the most important topic which is widely used in warehouse implementation that is Time/Date Dimension using Informatica.
It is  also widely acceptable as a Confirmed Dimension (A confirmed Dimension is a table whose attributes are widely referenced in multiple tables, as it can serve multiple fact tables).
Date-Time Dimension is used to analyze/report the data in terms of date and time up to its granular level.
Now, in our implementation we have taken Oracle as a Database and Informatica as a tool to achieve the basic functionality.

COMPLETE JOB SNAPSHOT


Job_Desc


We have taken source as s_date_source this source may not present in your database, we have used this source to pull data from oracle using a sequel query.
QUERY:-
SELECT sysdate+level,trunc(sysdate+level,’q’) FROM dual CONNECT  by level <366;
In our case we are loading our date-time dimension from the current date to the next complete year.
*trunc(sysdate+level,’q’) is the date passed to the function which will return the first date of every quarter, which further can be used to evaluate further columns.
Now to implement real logic we need to pull out one expression transformation from the palette.
monthOfQuater:-IIF(MOD(GET_DATE_PART(ora_date,’MM’),3)=0,3,MOD(GET_DATE_PART(ora_date,’MM’),3))
date_type:
IIF(To_char(ora_date,’DAY’)=’Saturday’) OR TO_Char(ora_date,’DAY’)=’Sunday’, ‘Weekend’, ‘Weekday’)
Try To use most of the basic function given by Informatica to achieve your functionality, some of the important ones are
GET_DATE_PART()
DATE_DIFF()
TO_CHAR()
TO_INT()
IIF()
O/P Rows 
out_date_iInteger,dayofyear,monthofYear,monthInChar,dayOfmonth,weekOfMonth,weekDayInChar,quaterOfYear,monthOfQuater,out_quater_first_date,dayOfQuater,day_type

1072013,181,7,Jul,1,1,Monday,3,1,07/01/2013,1,Weekday
2072013,182,7,Jul,2,1,Tuesday,3,1,07/01,2013,2,Weekday
31022013,276,10,oct,3,1,Thursday,4,1,10/01/2013,Weekday

This is one of the way to implement the basic Date-Time Dimension and you can further use various function given by the tool to achieve more functionality as per your requirements.
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Late Arriving Dimension in Talend

Image1
Hello readers,
                     In one of our previous posts we had already covered the concept and implementation of late arriving dimension using informatica.
So, directly we will show you how to achieve this functionality using Talend DI tool.

COMPONENTS REQUIRED

  • tOracleInput
  • tOracleOutput
  • tLogRow
  • tJavaFlex
  • tMap
Given below is the complete job description:-
JOB DESCRIPTION:-
  1. Create a first job that will bring the max surrogate key (using sequel query) from the production dimension table and save in one of context variable using tJavaFlex Component. In main code section of tJavaFlex write context.prod_skey=row4.prod_skey;
  2. Create a second job that runs after successful completion of first job and here bring the tOracleInput_1 component that will bring all the source data that resides into your staging area.
  3. Pull two more oracle input sources that will act as a lookup one for prod_dim table and other one is for cust_dim table.
  4. tMap Job Desc as described in the below figure
Use Left Outer Joiner Model at the left hand side in both the lookup i.e. for customer and product.
THIS JOB IS CREATED TO IMPLEMENT LATE ARRIVING DIMENSION CONCEPT FOR PROD_DIM ONLY.

5. The Top right corner output in tMap is used to populate your normal fact table but make sure to check whether your prod_dim skey must not be null.
6. The second insert is used  again to update your fact table but with the record that contains no surrogate key as late arriving dimension concept here you just increment your context variable and populate using ++context.prod_skey.
7. And Finally Insert a record in the product dimension for that just add one more output in tMap with the name like insert_prod with the same check constraint and use the incremented context variable.
8.In my job i have used tLogRow for logging purposes in real scenario you have to use tOracleOutPut component to be effective for DB.
9. For prod_dim insert output in tOracleOutput remember to use update or insert because if any changes will come then it will directly effect to your database as SCD1.
In case of any queries please do comment…..
 
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