Re: Do I just not understand count()?

I'm fairly sure you can't return a conditional count... count likes to
merely return the number of rows that match the query, which in this case is
all of them. I'm not sure exactly what it does with "a=1" though... I'm
guessing that it returns a boolean value, which means that it counts as a
row (only NULL values are not counted in count()).

If you're selecting other stuff, you won't be able to return more than one
row anyway... you'll have to either use a subquery or do a GROUP BY.

Greg

----- Original Message -----
From: "Ben" <bench(at)silentmedia(dot)com>
To: "Gregory Wood" <gregw(at)com-stock(dot)com>
Cc: "PostgreSQL-General" <pgsql-general(at)postgresql(dot)org>
Sent: Monday, April 08, 2002 2:45 PM
Subject: Re: [GENERAL] Do I just not understand count()?

> That's what I'd normally do to, but in this case I want to run a query
> more like
>
> select count(a=1), count(a=2) from t
>
> and I don't want to do multiple selects, because I'm selecting other stuff
> too, which takes time, and I figure as long as postgres is looking at
> those rows, it might as well tally up the counts of a=1 and a=2.
>
> On Mon, 8 Apr 2002, Gregory Wood wrote:
>
> > I don't think I've seen that particular syntax used before (I would say
> > select count(a) from t where a=1;), but since the query appears to work,
I
> > won't argue.
> >
> > Why do you think it should give you a result of 1? There are two rows
> > containing a value of 1 for a, hence it returns 2.
> >
> > Greg
> >
> > ----- Original Message -----
> > From: "Ben" <bench(at)silentmedia(dot)com>
> > To: <pgsql-general(at)postgresql(dot)org>
> > Sent: Monday, April 08, 2002 2:25 PM
> > Subject: [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....
> > >
> > >
> > > ---------------------------(end of
broadcast)---------------------------
> > > TIP 4: Don't 'kill -9' the postmaster
> > >
> >
>
>