Antw: LEFT JOIN

Antti Linno wrote:
> Greetings.
> I have a problem. I have 2 tables. E.g. work and workers. I want to
> select records, that 1st table has, and the second hasn't(both have id
> attribute). I mean I can't do it with is NULL, because those records don't
> exist. I was shown, how it is done with mysql

I think, the following select will solve your problem

select first.id
from first
except
second.id_first
from second;

>
> select first.id,second.id_first
> from first left join second on
> id=id_first where id_first is NULL;
>

This query should never give any result, because you require
id_first = id and id_first is null
but if id_first is null then it's equal to nothing,
and BTW it's also unequal to nothing.

> but when I tried it in psql, it said, not implemented.

Outer joins (left or right joins) are not implemented in PostgreSQL 7.0, but will
come in 7.1.

>
> Antti

Gerhard