I have a stored procedure that uses a table valued function which executes in 9 seconds. If I alter the table valued function and remove the where clause, the stored procedure executes in 3 seconds. If I add the where clause back, the query still executes in 3 seconds. I took a look at the execution plans and it appears that after I remove the where clause, the execution plan includes parallelism and the scan count for 2 of my tables drops for 50000 and 65000 down to 5 and 3. After I add the where clause back, the optimized execution plan still runs unless I run DBCC FREEPROCCACHE. Questions 1. Why would SQL Server start using the optimized execution plan for both queries only when I first remove the where clause? Is there a way to force SQL Server to use this execution plan? Also, this is a paramaterized all-in-one query that uses the (Parameter is null or Parameter) in the where clause, which I believe is bad for performance. RETURNS TABLE AS RETURN ( SELECT TOP (@PageNumber * @PageSize) CASE WHEN @SortOrder = 'Expensive' THEN ROW_NUMBER() OVER (ORDER BY SellingPrice DESC) WHEN @SortOrder = 'Inexpensive' THEN ROW_NUMBER() OVER (ORDER BY SellingPrice ASC) WHEN @SortOrder = 'LowMiles' THEN ROW_NUMBER() OVER (ORDER BY Mileage ASC) WHEN @SortOrder = 'HighMiles' THEN ROW_NUMBER() OVER (ORDER BY Mileage DESC) WHEN @SortOrder = 'Closest' THEN ROW_NUMBER() OVER (ORDER BY P1.Distance ASC) WHEN @SortOrder = 'Newest' THEN ROW_NUMBER() OVER (ORDER BY [Year] DESC) WHEN @SortOrder = 'Oldest' THEN ROW_NUMBER() OVER (ORDER BY [Year] ASC) ELSE ROW_NUMBER() OVER (ORDER BY InventoryID ASC) END as rn, P1.InventoryID, P1.SellingPrice, P1.Distance, P1.Mileage, Count(*) OVER () RESULT_COUNT, dimCarStatus.[year] FROM (SELECT InventoryID, SellingPrice, Zip.Distance, Mileage, ColorKey, CarStatusKey, CarKey FROM facInventory JOIN @ZipCodes Zip ON Zip.DealerKey = facInventory.DealerKey) as P1 JOIN dimColor ON dimColor.ColorKey = P1.ColorKey JOIN dimCarStatus ON dimCarStatus.CarStatusKey = P1.CarStatusKey JOIN dimCar ON dimCar.CarKey = P1.CarKey WHERE (@ExteriorColor is NULL OR dimColor.ExteriorColor like @ExteriorColor) AND (@InteriorColor is NULL OR dimColor.InteriorColor like @InteriorColor) AND (@Condition is NULL OR dimCarStatus.Condition like @Condition) AND (@Year is NULL OR dimCarStatus.[Year] like @Year) AND (@Certified is NULL OR dimCarStatus.Certified like @Certified) AND (@Make is NULL OR dimCar.Make like @Make) AND (@ModelCategory is NULL OR dimCar.ModelCategory like @ModelCategory) AND (@Model is NULL OR dimCar.Model like @Model) AND (@Trim is NULL OR dimCar.Trim like @Trim) AND (@BodyType is NULL OR dimCar.BodyType like @BodyType) AND (@VehicleTypeCode is NULL OR dimCar.VehicleTypeCode like @VehicleTypeCode) AND (@MinPrice is NULL OR P1.SellingPrice >= @MinPrice) AND (@MaxPrice is NULL OR P1.SellingPrice < @MaxPrice) AND (@Mileage is NULL OR P1.Mileage < @Mileage) ORDER BY CASE WHEN @SortOrder = 'Expensive' THEN -SellingPrice WHEN @SortOrder = 'Inexpensive' THEN SellingPrice WHEN @SortOrder = 'LowMiles' THEN Mileage WHEN @SortOrder = 'HighMiles' THEN -Mileage WHEN @SortOrder = 'Closest' THEN P1.Distance WHEN @SortOrder = 'Newest' THEN -[YEAR] WHEN @SortOrder = 'Oldest' THEN [YEAR] ELSE InventoryID END )