Re: Do I just not understand count()

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От Clinton Adams
Тема Re: Do I just not understand count()
Дата
Msg-id 20020408185126.022E347589D@postgresql.org
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Ответ на Do I just not understand count()?  (Ben <bench@silentmedia.com>)
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> If I have the table t defined as:
>
>  a
> ---
>  1
>  1
>  2
>
>
> and I say:
>
> select count(a=1) from t;
>
> should it give me 1 or 2 as a result? I'm getting 2, and I'd think I
> should get 1....
It will give you a result of 3, as a=1 does not toss out rows for which a <>
1.

You would need to add some parameters to limit the rows that count is
countin...
select count(a) from t where a = 1
would give you 2

select count(DISTINCT a) from t where a = 1
would give you 1




>
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