On 10/12/15 12:04 PM, Dara Unglaube wrote:
Greeetings. I'm trying to come up with a way to allow one column to have the same value up to two times, but no more than two times. I attempted adding a constraint to check the count of the value in the field - count (trsqqq) <=2 but aggregate functions are not allowed in constraints. Is there another way to do this? Any help would be greatly appreciated.
The safest bet is some kind of unique constraint. That would require having a separate count field, which you would limit to being 1 or 2 via a CHECK constraint. You could use a trigger to set the value based on what's already in the table.
By the way, the issue with doing a simple count is that it's not safe from race conditions, like an insert and a delete happening together.
-- Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX Experts in Analytics, Data Architecture and PostgreSQL Data in Trouble? Get it in Treble! http://BlueTreble.com -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
