Re: Optimal query suggestion needed

On Thu, Jun 17, 2004 at 14:46:08 +0000,
Interzone <lists(at)interzone(dot)gr> wrote:
> I want to create a view that will have:
> from table t0 the elements "code", "address" and "mun"
> from table t1 the elements "code" and "pname"
> from table t2 the total number of elements, and the total number of
> elements where avail = true, for every value t0_fk (foreign key to t0)
> and t1_fk (foreigh key to t1).
>
> After several attempts and changes as the requirements changed, I finaly
> came up with that :
>
> select t0.code, t0.address, t0.mun, t1.code as t1code, t1.pname
> count(t2.code) as t2total, (select count(t2.code) as t2avail from t2
> where t2.avail = true and t2.t0_fk=t0.code and t2.t1_fk = t1.code) as
> t2avail from t0, t1, t2 where t2.t0_fk = t0.code and t2.t1_fk=t1.code
> group by t0.code, t0.address, t0.mun, t1.code, t1.pname

This approach is actually pretty close. I think you just didn't pick a
good way to count the avail = true rows.
I think you can replace the above with:
select t0.code, t0.address, t0.mun, t1.code as t1code, t1.pname
count(t2.code) as t2total, count(case when t2.avail then 1 else NULL) as
t2avail from t0, t1, t2 where t2.t0_fk = t0.code and t2.t1_fk=t1.code
group by t0.code, t0.address, t0.mun, t1.code, t1.pname