How to Resolve the 'Must Declare the Scalar Variable' Error in SQL Server Stored Procedures?

Troubleshooting "Must Declare the Scalar Variable" Error in SQL Server

When using global input parameters (@RowFrom and @RowTo) within a stored procedure and compiling a SQL query using T-SQL, an error may occur if the parameters are used without declaring them as scalar variables inside the query.

To resolve this issue, it is important to declare the variables before using them. However, attempting to concatenate the integer parameter (@RowTo) with a string to assign it to a new variable is incorrect. Instead, use the CONVERT() function to convert the integer value to a string for concatenation.

For example, instead of:

SET @sql = N'DECLARE @Rt int; SET @Rt = ' + @RowTo;

Use:

SET @sql = N'DECLARE @Rt int; SET @Rt = ' + CONVERT(VARCHAR(12), @RowTo);

This ensures that the parameter is treated as a string when it is executed, avoiding the "Must declare the scalar variable" error.

Additionally, consider using proper parameterization to insert the parameter values into the query instead of concatenation. This practice enhances security by preventing SQL injection attacks. To parameterize the query, add the following line:

EXEC sys.sp_executesql @sql,
  N'@RowFrom int, @RowTo int',
  @RowFrom, @RowTo;

By following these recommendations, you can resolve the "Must declare the scalar variable" error and ensure the accurate execution of your SQL queries inside stored procedures.

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