Re: Do I just not understand count()
От | Jim Ballard |
---|---|
Тема | Re: Do I just not understand count() |
Дата | |
Msg-id | 004501c1df30$369c4600$8300a8c0@planet обсуждение исходный текст |
Ответ на | Do I just not understand count()? (Ben <bench@silentmedia.com>) |
Список | pgsql-general |
Try select sum(case when a=1 then 1 else 0 end), sum(case when a=2 the 1 else 0 end) from t; to get the number of occurrences of each value. Jim Ballard ----- Original Message ----- From: "Clinton Adams" <clinton@vote-smart.org> To: "Ben" <bench@silentmedia.com> Cc: <pgsql-general@postgresql.org> Sent: Monday, April 08, 2002 12:49 PM Subject: Re: [GENERAL] Do I just not understand count() > > 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 > > > > > > > > > > ---------------------------(end of broadcast)--------------------------- > > TIP 4: Don't 'kill -9' the postmaster > > ---------------------------(end of broadcast)--------------------------- > TIP 2: you can get off all lists at once with the unregister command > (send "unregister YourEmailAddressHere" to majordomo@postgresql.org) >
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