Outer Joins

How are outer joins implemented within PostgreSQL?
I would like to do a query of the form:

select a.x, b.y from a, b where a.x *= b.x;

The *= operator does not seem to exist. I've been
able to devise some clumsy workarounds by creating
temporary tables:

create table temp_table as
select a.x, b.y from a, b where a.x = b.x;

insert into temp_table
select x from a
except
select a.x from a, b where a.x = b.x;

Outer joins are apparently quite common, but I haven't
been able to find anything on this in either the users
guide, the draft of Bruce Momjian's upcoming book or the
Deja News archives.

Charles Mott