How do you do many to many table outer joins?

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  |
+----         


        

Answer 1

Working it out, you can start with your select. Don't include columns you don't want to ultimately see.

SELECT foo.fid, bar.value

Then we can do the WHERE clause, which can see is just as you expressed it.

SELECT foo.fid, bar.value  
WHERE bar.zid = 30

Now the tricky part to connect things together for our FROM clause, using LEFT JOINs because we want to see every fid, whether or not there are intermediate matches:

SELECT foo.fid, bar.value  
FROM foo  
LEFT JOIN foo2bar ON foo.fid = foo2bar.fid  
LEFT JOIN bar ON foo2bar.bid = bar.bid  
WHERE bar.zid = 30
OR bar.zid IS NULL