To explain by example, take two tables, A and B

Table A
id  foo
 1   x
 2   y
 3   z


Table B
id  aid bar
 1   3   50
 2   1  100

An example join

SELECT foo, bar FROM a, b WHERE a.id = b.aid;

Garners a result of

foo  bar
 z    50
 x   100

What I would like to do is get all values of foo and for any instances where there isn't a corresponding bar value, return 0 for that column.

My best guess was something along the lines of

SELECT foo, bar AS br FROM a, b 
WHERE a.id = b.aid 
OR a.id NOT IN (SELECT aid FROM b);

But that returns duplicates and non-zero values for bar.

Possible?