Re: Question about joins, left outer and others - Mailing list pgsql-general

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

> jross@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