Re: Question about joins, left outer and others

Jeff Ross <jross(at)wykids(dot)org> writes:
> To get the output I want above, I'd think I'd need to do a left outer join
> like this:

> jross(at)wykids localhost# select ed_cat_name as "Level", pp_ed_cat_subject as
> "Subject", pp_ed_cat_institution as "Institution" from
> education_categories left outer join people_education_categories on
> (ed_cat_id = pp_ed_cat_id) where pp_ed_cat_pp_id = 1796;

This query is actually equivalent to a plain join. The reason is that
no null-extended row can possibly satisfy the WHERE clause, since the
WHERE is constraining a field from the inner side of the join. Remember
WHERE filters the output of the join.

Possibly what you want is

select ... from
education_categories left outer join people_education_categories on
(ed_cat_id = pp_ed_cat_id and pp_ed_cat_pp_id = 1796);

regards, tom lane