Adding missing rows in table in 1 select (+ join) command

Hi all! Here's what I need to do :

I have two tables :
A B
a b c d
---- ----
1 z 1 k
2 x 5 l
3 c 6 j

I need a SELECT with JOIN that would give me :
A
a b
----
1 z
2 x
3 c
5 NULL
6 NULL

so I need to add the missing rows from the A.a and B.c JOIN,
how can I do that ?

I can't use a UNION because I can't use MySQL version 4.

Thanks,

Simon

The only way I can think of doing this without a UNION is writing a procedure and poplulating a temporary table then selecting from that.

If it was SQL Server then I could do this

select case
when a.a is null then b.c
when a.a is not null then a.a
end, a.b
from B b full outer join A a
on a.a = b.c
order by 1

I don't know whether you have equivalent of this in mysql.