Question

In the below SQL Statement, should I be using DISTINCT as I have a Group By in my Where Clause? Thoughts?

SELECT [OrderUser].OrderUserId, ISNULL(SUM(total.FileSize), 0), ISNULL(SUM(total.CompressedFileSize), 0)
FROM 
(
 SELECT DISTINCT ProductSize.OrderUserId, ProductSize.FileInfoId, 
 CAST(ProductSize.FileSize AS BIGINT) AS FileSize, 
 CAST(ProductSize.CompressedFileSize AS BIGINT) AS CompressedFileSize
 FROM ProductSize WITH (NOLOCK)
 INNER JOIN [Version] ON ProductSize.VersionId = [Version].VersionId
) AS total RIGHT OUTER JOIN [OrderUser] WITH (NOLOCK) ON total.OrderUserId = [OrderUser].OrderUserId
WHERE NOT ([OrderUser].isCustomer = 1 AND [OrderUser].isEndOrderUser = 0 OR [OrderUser].isLocation = 1) 
AND [OrderUser].OrderUserId = 1
GROUP BY [OrderUser].OrderUserId

Answer 1

Since the question wasn’t written as clearly as possible, I am assuming you are asking if the distinct is extraneous due to the group by that exists.

If the inner query returns multiple records due to the inner join, you will need a distinct there. Otherwise the right outer join will join on more records than you intend and things like SUM() will not return the same values.

So DISTINCT is not extraneous.