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Editorial Team
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Asked: 2026-05-14T15:45:57+00:00

Usually when looking for some items not showing up in the other table, we

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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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1 Answer

  1. Editorial Team

    When you call DISTINCT on a result, it required a scan through the list in order to find and remove the duplicated. This is a slow operation, and there is a good chance that the query as a whole will be faster without it.

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