Warning: Null value is eliminated by an aggregate or other SET operation in Aqua Data Studio

You would mostly be using COUNT to summarize over a UID. Therefore

COUNT([uid]) will produce the warning:

Warning: Null value is eliminated by an aggregate or other SET operation.

whilst being used with a left join, where the counted object does not exist.

Using COUNT(*) in this case would also render incorrect results, as you would then be counting the total number of results (ie parents) that exist.

Using COUNT([uid]) IS a valid way of counting, and the warning is nothing more than a warning. However if you are concerned, and you want to get a true count of uids in this case then you could use:

SUM(CASE WHEN [uid] IS NULL THEN 0 ELSE 1 END) AS [new_count]

This would not add a lot of overheads to your query.
(tested mssql 2008)

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