Monday, August 13, 2007

FAQ on Stored Procedure in SQL Server

FAQ on Stored Procedure in SQL Server

49. 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.

50. 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

51. How do I mark the stored procedure to automatic execution?
You can use the sp_procoption system stored procedure to mark the
stored procedure to automatic execution when the SQL Server will start.
Note. Only objects in the master database owned by dbo can have the
startup setting changed and this option is restricted to objects that
have no parameters.
USE master
EXEC sp_procoption 'indRebuild', 'startup', 'true')



52. How can you optimize a stored procedure?

53. 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.

54. 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.

55. 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)

56. 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).

57. 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.

58. How to find out which stored procedure is recompiling? How to stop
stored procedures from recompiling?

59. 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.

60. 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.

61. 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

62. 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?

63. What do you do when one procedure is blocking the other?

64. How you will return XML from Stored Procedure?

65. 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) factorial="1" 1="1" previous_number="@base_number-1" factorial="-1)" factorial="@factorial*@base_number">

that can be called from T-SQL, just the way we call normal stored
procedures using the EXEC statement.

68. 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"

69. 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.

70. 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 (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.


For More SQL SERVER Frequently Asked Interview Questions

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