SQL Declare Variables

问题:

Can anyone check on my statement...

DECLARE @tblName varchar(MAX), 
        @strSQL varchar(MAX)

SET @tblName ='SELECT DISTINCT o.name as TableName 
                 FROM sysobjects o 
                 JOIN sysindexes x on o.id = x.id  
                WHERE o.name LIKE ''%empty%'''  

SET @strSQL = 'INSERT INTO @tblName VALUES(''trylng'', ''1'')'
EXEC (@strSQL)

my error is...

Msg 1087, Level 15, State 2, Line 1
Must declare the table variable "@tblName".

回答1:

Your @tblName property exists at the outer scope - the scope of your "normal" code lines - but not at the inner scope of the SQL you're constructing in the string there....

You need to change your lines to read:

SET @strSQL = 'INSERT INTO ' + @tblName + ' VALUES(''trylng'', ''1'')'

and then it should work just fine.

Also, you're not mentioning your SQL Server version - but as of SQL Server 2005 or newer, you should stop using sysobjects and sysindexes - instead, use the new sys schema that contains more or less the same information - but more easily available. Change your query to:

SET @tblName ='SELECT DISTINCT t.name as TableName 
               FROM sys.tables t
               INNER JOIN sys.indexes i on i.object_id = t.object_id  
               WHERE t.name LIKE ''%empty%'''  

See MSDN: Querying the SQL Server System Catalog for a lot more information on what's available in the new sys schema and how to make the most of it!

As "rsbarro" pointed out : putting this SQL statement here into quotes is odd - are you executing this statement using EXEC(...), too?? But then how do you assign the value back to the @tblName property? Doesn't really make sense.....

If you want to actually run this query to get a value, you should have something like this:

 SELECT TOP 1 @tblName = t.name
 FROM sys.tables t
 INNER JOIN sys.indexes i on i.object_id = t.object_id  
 WHERE t.name LIKE '%empty%'

You need to have a TOP 1 in there to be sure to get just a single value - otherwise this statement could fail (if multiple rows are selected).

回答2:

Not sure exactly what you're trying to do, but I think you want something like this:

DECLARE @tblName varchar(MAX), @strSQL varchar(MAX)
SET @tblName = 
    (select distinct o.name as TableName 
     from sysobjects o 
     join sysindexes x on o.id = x.id  
     where o.name LIKE '%empty%')
SET @strSQL = 'INSERT INTO [' + @tblName + '] VALUES(''trylng'', ''1'')'
exec (@strSQL)

That being said, there are still a couple things to watch out for here. You need to handle the condition where the SELECT DISTINCT returns anything other than a single record. Also, I don't really understand the need to build dynamic SQL (in @strSQL) when @tblName will always have the same value (since there are no variables used in the WHERE clause).