From: | Patrick Welche <prlw1(at)newn(dot)cam(dot)ac(dot)uk> |
---|---|
To: | Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: trivial sql help |
Date: | 2002-10-10 17:52:56 |
Message-ID: | 20021010185256.T6842@quartz.newn.cam.ac.uk |
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Thread: | |
Lists: | pgsql-general |
On Thu, Oct 10, 2002 at 09:14:41AM -0700, Stephan Szabo wrote:
>
> On Thu, 10 Oct 2002, Patrick Welche wrote:
>
> > update rawrequest
> > set cid=(select pc.c
> > from pers_comp as pc
> > where pc.p=pid
> > group by pc.c
> > having count(pc.c)=1
> > )
> > where pr
> > ;
> >
> > ERROR: More than one tuple returned by a subselect used as an expression.
> >
> > pid, pc.p, pc.c, cid are all integers. pc just has 2 columns p and c.
> >
> > I thought putting the count()=1 in there would force a single tuple..
>
> No, that'll limit you only to groups having a count of 1. It'll still
> give multiple groups. You could probably use limit to get 1 row, but
> what's the actual behavior you want the update to have?
pers_comp relates person to computer. 99% of students have 1 computer =>
only one pers_comp(p,c) entry. I just wanted to fill in the computer's id
into the request of a given person for the simple case.
Anyway, I was just having brain failure.. as you have all happily explained
away the error message, I'll try again..
Cheers,
Patrick
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