如何在SQL 2005中将变量设置为表名称的SQL查询结果的变量

Question

I'm currently having trouble writing a stored procedure and setting the value of a variable of type int to the results of a select statement with a variable as the tablename. I've looked at old threads and tried multiple methods, but no luck. If I'm not getting an error regarding the tablename, I end up getting an error with a variable conversion issue. I've been working on this for too long and any help would be appreciated. Below is a portion of my code. Thanks

DECLARE @BATCHNUMBER VARCHAR  --value set in earlier code
DECLARE @ETABLE VARCHAR(50); --the table name
DECLARE @FIRSTDOCID INT;      
SET @ETABLE = 'tablename_' + @BATCHNUMBER; --CREATE FIRST TABLE NAME

SELECT @FIRSTDOCID = MIN(D0CID) FROM @ETABLE

The error I get is: Must declare the table variable "@ETABLE"

Answer 1

You are trying to select from a VARCHAR , not a table. The only way to make this work is by using Dynamic SQL.

DECLARE @SQL NVARCHAR(250);
SET @SQL = 'SELECT @OUTPUT = MIN(D0CID) FROM ' + QuoteName(@ETABLE);
EXEC sp_executeSql @SQL, N'@output INT OUTPUT', @FIRSTDOCID OUTPUT;

SELECT @FIRSTDOCID;

However, I would not suggest using Dynamic SQL as this often leads to SQL injection.

Answer 2

You'll probably have to do something like use exec if you're dynamically building the query:

SET @QUERY = "SELECT" + ...etc.
exec(@QUERY)

Since ETABLE is a varchar, and not, as expected, a 'table variable'.