On 6/21/07, danmcb <danielmcbrearty@xxxxxxxxx> wrote:
Hi I have two tables, say A and B, that have a many-to-many relationship, implemented in the usual way with a join table A_B. How can I economically find all the rows in table A whose id's are not in A_B at all (i.e. they have zero instances of B associated)?
Use a left join. For instance, say there are a.id and b.id columns, which are the primary keys in A and B respectively. Also say A_B contains columns aid and bid which reference a.id and b.id respectively.
SELECT * FROM A LEFT JOIN A_B ON (A.ID = A_B.AID) WHERE A_B.BID IS NULL;
- Josh
