Question

I have 3 tables, foo, foo2bar, and bar. foo2bar is a many to many map between foo and bar. Here are the contents.

select * from foo +------+ | fid  | +------+ |    1 | |    2 | |    3 | |    4 | +------+  select * from foo2bar +------+------+ | fid  | bid  | +------+------+ |    1 |    1 | |    1 |    2 | |    2 |    1 | |    2 |    3 | |    4 |    4 | +------+------+  select * from bar +------+-------+------+ | bid  | value | zid  | +------+-------+------+ |    1 |     2 |   10 | |    2 |     4 |   20 | |    3 |     8 |   30 | |    4 |    42 |   30 | +------+-------+------+ 

What I want to request is, ‘Give me a list of all the fid and values with zid of 30’

I expect an answer for all the fids, so the result would look like:

+------+--------+ | fid  | value  | +------+--------+ |    1 |   null | |    2 |      8 | |    3 |   null | |    4 |     42 | +------+--------+ 

Answer 1

SELECT * FROM foo   LEFT OUTER JOIN (foo2bar JOIN bar ON (foo2bar.bid = bar.bid AND zid = 30))   USING (fid); 

Tested on MySQL 5.0.51.

This is not a subquery, it just uses parentheses to specify the precedence of joins.