Yes, if you are concerned about the performance of updates/deletes on the departments table. The reason the system doesn't make such an index automatically is that there are common scenarios where you seldom or never update the master table, and so the index wouldn't repay the cost it creates for updates of the slave table.
Thanks for the explanations :-) regards -- Arnau ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
