Re: count() and multiple tables

Stephan Szabo wrote:
>
> On Mon, 19 Mar 2001, Joseph Shraibman wrote:
>
> > I want to select all the entries from d that have at least one
> > corresponding entry in u that meets my conditions. The problem is that
> > count(*) is returning the number of corresponding entries in u, and I
> > want only the number of entries in d. How do I do this?
> >
> >
> > create table d(
> > id int primary key,
> > status int default 1
> > );
> >
> > create table a(
> > key int primary key,
> > status int default 1
> > );
> >
> > create table u(
> > dkey int not null,
> > akey int not null,
> > b bool DEFAULT false,
> > status int default 1,
> > primary key (dkey, akey)
> > );
> >
> > insert into d values (1, 2);
> >
> > insert into a values (1, 3);
> > insert into a values (2, 3);
> > insert into a values (3, 3);
> >
> > insert into u values(1,1,false,2);
> > insert into u values(1,2,false,1);
> > insert into u values(1,3,false,2);
> >
> > select count(*) from d where status = 2 and d.id = u.dkey and u.status =
> > 2 and not u.b and u.akey = a.key and a.status = 3;
>
> And postgres tries to be helpful again... :( [I *really* dislike this
> adding to from list thing] Technically the above should be illegal
> because no from list contains u or a. Postgres is adding them to the
> from list for you.
>
I get the same result if I do:
select count(d.id) from d where status = 2 and d.id = u.dkey and
u.status = 2 and not u.b and u.akey = a.key and a.status = 3;

So in standard SQL all the tables you join accross are required to be in
the FROM?

> I think you want something like (untested):
> select count(*) from d where status=2 and
> exists (
> select * from u, a where u.dkey=d.id and u.status=2 and
> no u.b and u.akey=a.key and a.status=3
> );

That works, but I thought there might be a better way because it looks
like that will get all the data out of the table and throw it away right
after.

--
Joseph Shraibman
jks(at)selectacast(dot)net
Increase signal to noise ratio. http://www.targabot.com