How to Handle Expression Results as Stored Procedure Parameters in SQL Server?

SQL Server Stored Procedure Parameter Challenges

Using parameters with stored procedures streamlines database development. However, directly embedding expression or function results within a stored procedure's parameter list can lead to issues. For instance, the following code:

<code class="language-sql">DECLARE @pID int;
SET @pID = 1;
EXEC WriteLog 'Component', 'Source', 'Could not find given id: ' + CAST(@pID AS varchar);</code>

fails in SQL Server 2005 and earlier, generating a "Msg 102" syntax error. This limitation stems from how SQL Server handles parameters.

The Solution: Intermediate Variables

The workaround involves using an intermediate variable. SQL Server doesn't allow direct embedding of expression results as parameters; however, an intermediate variable provides a solution.

The corrected syntax is:

<code class="language-sql">DECLARE @pID INT;
SET @pID = 1;

/* For SQL Server 2008 and later;  For earlier versions, these must be separate statements */
DECLARE @string VARCHAR(50) = 'Could not find given id: ' + CAST(@pID AS VARCHAR(11));

EXEC WriteLog
  'Component',
  'Source',
  @string;</code>

By assigning the expression's output ('Could not find given id: ' CAST(@pID AS VARCHAR(11))) to the @string variable, we can then pass @string as a parameter to WriteLog, effectively incorporating the expression's result. Note the important distinction for versions prior to SQL Server 2008 requiring separate DECLARE and SET statements.

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