Execution Plan Optimization when where clause is removed then added back
- by nmushov
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
)
