I'm having the following tables:

Table a
+-------+------------------+------+-----+
| Field | Type             | Null | Key |
+-------+------------------+------+-----+
| bid   | int(10) unsigned | YES  |     |
| cid   | int(10) unsigned | YES  |     |
+-------+------------------+------+-----+

Table b
+-------+------------------+------+
| Field | Type             | Null |
+-------+------------------+------+
| bid   | int(10) unsigned | NO   |
| cid   | int(10) unsigned | NO   |
| data  | int(10) unsigned | NO   |
+-------+------------------+------+

When I want to select all rows from b where there's a corresponding bid/cid-pair in a, I simply use a natural join SELECT b.* FROM b NATURAL JOIN a; and everything is fine.

When a.bid or a.cid is NULL, I want to get every row where the other column matches, e.g. if a.bid is NULL, I want every row where a.cid=b.cid, if both are NULL I want every column from b.

My naive solution was this:

SELECT DISTINCT b.* FROM b JOIN a ON ( ISNULL(a.bid) OR a.bid=b.bid ) AND (ISNULL(a.cid) OR a.cid=b.cid )

Is there any better way to to this?