How to Correctly Pass Expression Results as Stored Procedure Parameters?

SQL Server Stored Procedure Parameter Pitfalls: Handling Expression Results

Passing the output of expressions or function calls directly as parameters in SQL Server stored procedures often leads to errors. Let's illustrate this with a common issue encountered in SQL Server 2005:

The following code snippet generates a syntax error:

DECLARE @pID int;
SET @pID = 1;
EXEC WriteLog 'Component', 'Source', 'Could not find given id: ' + CAST(@pID AS varchar);

This results in the error:

<code>Msg 102, Level 15, State 1, Line 4
Incorrect syntax near '+'.</code>

The root cause? SQL Server doesn't allow direct use of expressions or function results within the stored procedure's parameter list. The solution involves an intermediate variable.

Here's the corrected approach:

DECLARE @pID INT;
DECLARE @logMessage VARCHAR(50);

SET @pID = 1;
SET @logMessage = 'Could not find given id: ' + CAST(@pID AS VARCHAR(11));
EXEC WriteLog 'Component', 'Source', @logMessage;

This revised code assigns the expression's result to @logMessage, which is then correctly recognized as the third parameter. The stored procedure executes without errors.

It's crucial to note: This restriction applies solely to parameter values; expressions within the stored procedure's body are unaffected.

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