DECLARE @IntVariable INT;
DECLARE @SQLString NVARCHAR(500);
DECLARE @ParmDefinition NVARCHAR(500);
DECLARE @ParametroProvaValore int

SET @ParametroProvaValore= NULL

/* Build the SQL string one time. */
IF @ParametroProvaValore IS NULL
BEGIN
   SET @SQLString =
     N'SELECT * FROM AdventureWorks.Sales.Store WHERE SalesPersonID = @SalesID';
END

IF @ParametroProvaValore IS NOT NULL
BEGIN
   SET @SQLString =
     N'SELECT * FROM AdventureWorks.Sales.Store WHERE SalesPersonID = @SalesID AND Colonna = @ParametroProva';
END

/* Specify the parameter format one time. */
SET @ParmDefinition = N'@SalesID int, @ParametroProva int';

/* Execute the string with the first parameter value. */
SET @IntVariable = 275;
EXECUTE sp_executesql @SQLString, @ParmDefinition,                      
                      @SalesID = @IntVariable,@ParametroProva = @ParametroProvaValore;

/* Execute the same string with the second parameter value. */
SET @IntVariable = 276;
EXECUTE sp_executesql @SQLString, @ParmDefinition,
                      @SalesID = @IntVariable,@ParametroProva = @ParametroProvaValore;