group by weirdness

Could someome explain these error messages to me? Why am I being asked to group by j.id?
And why is the subquery worried about ml.oid if ml.oid is used in an aggregate?

Follows: script, then output.

select version();
create table j (id int, created timestamp default current_timestamp, fkey int);
create table mj (jid int, mid int);
create table ml (jid int, created timestamp default current_timestamp, state int);

insert into j (id, fkey) values (1, 1);
insert into j (id, fkey) values (2, 1);

insert into mj values(1, 1);
insert into mj values(1, 2);
insert into mj values(2, 3);
insert into mj values(2, 4);
insert into mj values(2, 5);

insert into ml(jid, state) values (1, 2);
insert into ml(jid, state) values (1, 2);
insert into ml(jid, state) values (1, 2);
insert into ml(jid, state) values (1, 2);
insert into ml(jid, state) values (1, 11);
insert into ml(jid, state) values (2, 2);
insert into ml(jid, state) values (2, 2);
insert into ml(jid, state) values (2, 11);

select j.id, j.created, count(mj.mid),
(select count(ml.oid) where ml.state <> 11),
(select count(ml.oid) where ml.state IN(2,5) )
FROM j, mj, ml WHERE j.fkey = 1 AND mj.jid = j.id AND ml.jid = j.id ;

select j.id, j.created, count(mj.mid),
(select count(ml.oid) where ml.state <> 11),
(select count(ml.oid) where ml.state IN(2,5) )
FROM j, mj, ml WHERE j.fkey = 1 AND mj.jid = j.id AND ml.jid = j.id
group by j.id, j.created;

drop table j;
drop table mj ;
drop table ml;

===================================================================================================

playpen=# select version();
version
---------------------------------------------------------------------
PostgreSQL 7.1.3 on i686-pc-linux-gnu, compiled by GCC egcs-2.91.66
(1 row)

playpen=# create table j (id int, created timestamp default current_timestamp, fkey int);
CREATE
playpen=# create table mj (jid int, mid int);
CREATE
playpen=# create table ml (jid int, created timestamp default current_timestamp, state int);
CREATE
playpen=#
playpen=# insert into j (id, fkey) values (1, 1);
<snip>
playpen=# insert into ml(jid, state) values (2, 11);
INSERT 329676 1
playpen=#
playpen=# select j.id, j.created, count(mj.mid),
playpen-# (select count(ml.oid) where ml.state <> 11),
playpen-# (select count(ml.oid) where ml.state IN(2,5) )
playpen-# FROM j, mj, ml WHERE j.fkey = 1 AND mj.jid = j.id AND ml.jid = j.id ;
ERROR: Attribute j.id must be GROUPed or used in an aggregate function
playpen=#
playpen=# select j.id, j.created, count(mj.mid),
playpen-# (select count(ml.oid) where ml.state <> 11),
playpen-# (select count(ml.oid) where ml.state IN(2,5) )
playpen-# FROM j, mj, ml WHERE j.fkey = 1 AND mj.jid = j.id AND ml.jid = j.id
playpen-# group by j.id, j.created;
ERROR: Sub-SELECT uses un-GROUPed attribute ml.oid from outer query
playpen=#
playpen=# drop table j;
DROP
playpen=# drop table mj ;
DROP
playpen=# drop table ml;
DROP

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