Must declare the scalar variable

Question

@RowFrom int

@RowTo int

are both Global Input Params for the Stored Procedure, and since I am compiling the SQL query inside the Stored Procedure with T-SQL then using Exec(@sqlstatement) at the end of the stored procedure to show the result, it gives me this error when I try to use the @RowFrom or @RowTo inside the @sqlstatement variable that is executed.. it works fine otherwise.. please help.

"Must declare the scalar variable "@RowFrom"."

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Also, I tried including the following in the @sqlstatement variable:

'Declare @Rt int'
'SET @Rt = ' + @RowTo

but @RowTo still doesn't pass its value to @Rt and generates an error.

Answer 1

You can't concatenate an int to a string. Instead of:

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

You need:

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

To help illustrate what's happening here. Let's say @RowTo = 5.

DECLARE @RowTo int;
SET @RowTo = 5;

DECLARE @sql nvarchar(max);
SET @sql = N'SELECT ' + CONVERT(varchar(12), @RowTo) + ' * 5';
EXEC sys.sp_executesql @sql;

In order to build that into a string (even if ultimately it will be a number), I need to convert it. But as you can see, the number is still treated as a number when it's executed. The answer is 25, right?

In your case you don't really need to re-declare @Rt etc. inside the @sql string, you just need to say:

SET @sql = @sql + ' WHERE RowNum BETWEEN ' 
    + CONVERT(varchar(12), @RowFrom) + ' AND ' 
    + CONVERT(varchar(12), @RowTo);

Though it would be better to have proper parameterization, e.g.

SET @sql = @sql + ' WHERE RowNum BETWEEN @RowFrom AND @RowTo;';

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