


How Can I Properly Use Table Variables in Dynamic SQL Statements in SQL Server 2008?
Dynamic SQL and Table Variables in SQL Server 2008: A Solution
SQL Server 2008 presents challenges when using table variables within dynamic SQL. This article addresses this issue and offers a practical workaround.
The Problem: Undeclared Table Variables
A common scenario involves a stored procedure attempting to execute a dynamic SQL query that references locally declared table variables. The result is often an error indicating that these variables are undeclared within the dynamic SQL context. Consider this example:
DECLARE @col_name NVARCHAR(MAX), @sqlstat NVARCHAR(MAX), @curr_row INT, @curr_row1 INT; -- ... other code to populate @curr_row and @curr_row1 ... DECLARE @RelPro TABLE (RowID INT, Assoc_Item_1 INT, Assoc_Item_2 INT, ...); DECLARE @TSku TABLE (tid INT, relsku INT); -- ... populate @RelPro and @TSku ... SET @col_name = 'Assoc_Item_' + CONVERT(NVARCHAR(2), @curr_row1); SET @sqlstat = 'UPDATE @RelPro SET ' + @col_name + ' = (SELECT relsku FROM @TSku WHERE tid = ' + CONVERT(NVARCHAR(2), @curr_row1) + ') WHERE RowID = ' + CONVERT(NVARCHAR(2), @curr_row); EXEC sp_executesql @sqlstat;
This code will fail with the error:
<code>Must declare the table variable "@RelPro". Must declare the table variable "@TSku".</code>
The Solution: Table-Valued Parameters
SQL Server 2008 and later versions provide a robust solution: table-valued parameters. While these parameters prevent direct modification of the table data within the dynamic SQL, they allow referencing the table's contents.
To adapt the above code, we'll create a user-defined table type and then use it as a parameter:
-- Create a user-defined table type CREATE TYPE MySkuTable AS TABLE (tid INT, relsku INT); GO -- Stored Procedure using Table-Valued Parameter CREATE PROCEDURE UpdateRelPro (@TSku MySkuTable READONLY, @curr_row INT, @curr_row1 INT) AS BEGIN DECLARE @col_name NVARCHAR(MAX), @sqlstat NVARCHAR(MAX); SET @col_name = 'Assoc_Item_' + CONVERT(NVARCHAR(2), @curr_row1); SET @sqlstat = N'UPDATE @RelPro SET ' + @col_name + N' = (SELECT relsku FROM @TSku WHERE tid = ' + CONVERT(NVARCHAR(2), @curr_row1) + N') WHERE RowID = ' + CONVERT(NVARCHAR(2), @curr_row); -- Declare @RelPro within the procedure DECLARE @RelPro TABLE (RowID INT, Assoc_Item_1 INT, Assoc_Item_2 INT, ...); -- ... populate @RelPro ... EXEC sp_executesql @sqlstat, N'@RelPro MyTable READONLY', @RelPro = @RelPro; END; GO -- Example Usage: DECLARE @TSku MySkuTable; INSERT INTO @TSku VALUES (1, 10), (2, 20); DECLARE @RelPro TABLE (RowID INT, Assoc_Item_1 INT, Assoc_Item_2 INT); INSERT INTO @RelPro VALUES (1, NULL, NULL); EXEC UpdateRelPro @TSku, 1, 1;
This revised approach uses sp_executesql
correctly, passing the table-valued parameter @TSku
and the table variable @RelPro
(declared inside the procedure) as parameters. The READONLY
keyword prevents modification of the input table. Remember to declare @RelPro
inside the stored procedure. This technique allows safe and effective use of table variables within dynamic SQL.
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