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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