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Dynamic SQL

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Beginer2012
Starting Member

45 Posts

Posted - 2012-06-11 : 08:56:20

Hello,

Upon executing the following code I get this error:
-------------------------------------------------
Msg 137, Level 15, State 1, Line 1
Must declare the scalar variable "@MyCount".
-------------------------------------------------

I need to store the count in a variable dynamically to genrate complicated report.
Any sugestions ?

Thank you

DECLARE @MyCount INT
DECLARE @MyTable VARCHAR(10)
DECLARE @SqlCmd NVARCHAR(500)

SET @Mytable = 'test'

SET @SqlCmd = 'SELECT @MyCount =COUNT(*) FROM ' + @MyTable

EXECUTE (@SqlCmd)

sunitabeck
Master Smack Fu Yak Hacker

5155 Posts

Posted - 2012-06-11 : 09:22:42

You should use the sp_executesql interface to get data out from the dynamic SQL query. http://msdn.microsoft.com/en-us/library/ms188001.aspx

Your query would be something like this (untested):

DECLARE @MyCount INT
DECLARE @MyTable VARCHAR(10)
DECLARE @SqlCmd NVARCHAR(500)

SET @Mytable = 'test'

SET @SqlCmd = 'SELECT @TheCount =COUNT(*) FROM ' + @MyTable

EXEC sp_executesql  
	@stmt = @SqlCmd, 
	@params = N'@TheCount as int OUTPUT', 
	@TheCount = @MyCount OUTPUT;
select @MyCount;

Note, OUTPUT specified in two places. Also, I changed the variable name in the dynamic SQL to @TheCount just to show the distinction.

[Insert usual advice about avoiding dynamic sql if at all possible here]

Beginer2012
Starting Member

45 Posts

Posted - 2012-06-11 : 09:25:18

Thank you very much for your help.

robvolk
Most Valuable Yak

15732 Posts

Posted - 2012-06-11 : 12:19:21

If all you need is a count of all rows in the table:

DECLARE @MyTable varchar(100), @MyCount bigint
SELECT @MyCount=rows FROM sys.partitions WHERE OBJECT_NAME(object_id)=@MyTable AND index_id<2

As sunita suggested, there's no dynamic SQL needed.

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