Re: JOIN and aggregate problem

On Fri, 20 Feb 2009 11:15:09 -0800 (PST)
Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> wrote:

> On Fri, 20 Feb 2009, Tarlika Elisabeth Schmitz wrote:
>
> > I have 2 tables T1 and T2
> >
> > T1 has the columns: D, S, C. The combination of D,S,C is unique.
> > T2 has the columns: D, S, C, and boolean X. The combination of
> > D,S,C is not unique.
> >
> > I need to produce the following result for every occurrence of T1:
> > D,S,C, COUNT
> >
> > COUNT is the number of matching D,S,C combinations in T2 where X =
> > true. There might be no matching pair in T2 or there might be match
> > but X is false.
> >
>
> Maybe something like one of these barely tested queries?
>
> select d, s, c, sum(case when t2.x then 1 else 0 end)
> from t1 left outer join t2 using(d,s,c)
> group by d, s, c;

this works

> or
>
> select d,s,c,
> (select count(*)
> from t2
> where t2.d=t1.d and t2.s=t1.s and t2.c=t1.c and t2.x)
> from t1;

this works too

From a performance point of view, is one preferable to the other?

Many thanks for your help!

--
Tarlika Elisabeth Schmitz