In SQL, why is "Distinct" not used in a subquery, when looking for some items "not showing up" in th
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Published on 2010-04-24T14:54:46Z
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Usually when looking for some items not showing up in the other table, we can use:
select * from gifts where giftID not in (select giftID from sentgifts);
or
select * from gifts where giftID not in (select distinct giftID from sentgifts);
the second line is with "distinct" added, so that the resulting table is smaller, and probably let the search for "not in" faster too.
So, won't using "distinct" be desirable? Often than not, I don't see it being used in the subquery in such a case. Is there advantage or disadvantage of using it? thanks.
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