Thread: problems with left outer join

Hi,

I would like to make a left outer join between two tables (A and B) and then only select rows of table A which do not apply on the join condition (where B is null)

simple example:

create table A(
 id int primary key
);

create table B(
 id int primary key
);

insert into A values(1);
insert into A values(2);
insert into B values(1);

The goal is now to make a join between A and B and to select only the row from A with the id = 2 (because there is no corresponding id in Table B)

So I tried:

select *
from A t1 left outer join B t2 on t1.id = t2.id
where t2.id = null

but I dont get any row returned. I expect the result: 2 | NULL


if I execute

select *
from A t1 left outer join B t2 on t1.id = t2.id

I get:
1) 2 | NULL
2) 1 | 1

what am I doing wrong ?
thanx in advance,
Andreas

On 10:13 Thu 05 Oct     , Andreas Andreakis wrote:
> Hi,
>
> So I tried:
>
> select *
> from A t1 left outer join B t2 on t1.id = t2.id
> where t2.id = null

Swap '=' with 'is'

Regards,
Andy





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"Andreas Andreakis" <andreas.andreakis@googlemail.com> writes:
> So I tried:

> select *
> from A t1 left outer join B t2 on t1.id = t2.id
> where t2.id = null

You need "IS NULL", not "= NULL".  See
http://www.postgresql.org/docs/8.1/static/functions-comparison.html

            regards, tom lane