Re: Question about joins, left outer and others

Tom Lane wrote:
> 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
>

Thanks, Tom and Andy.  This is exactly what I was missing.

Jeff Ross