On Fri, Jan 26, 2007 at 10:41:26 +0100, Tomas Vondra <[EMAIL PROTECTED]> wrote: > > in our application we need to implement a constraint that enforces 'at > most N rows with this value', that is we have a table with 'flag' column > and for each value there should be at most 10 rows (for example, the > exact number does not matter).
Another approach is to add a instance number column and constrain that value to be between 1 and 10. And make value and instance number unique. You'll need to do a bit more work when inserting new rows than normal (to find a free instance number). This should be very robust against getting in a bad state. If you go with enforcing the condition with a trigger you need to be careful about simultaneous inserts and visibility. ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly