--- Bruno Wolff III <bruno@xxxxxxxx> wrote: > On Fri, Dec 30, 2005 at 13:30:40 -0800, > CSN <cool_screen_name90001@xxxxxxxxx> wrote: > > I have three columns, and one of them can be null. > I'd > > like to create a unique constraint across all > three > > columns and allow only one null value. e.g. > > > > a|b|c > > abc|123|null > > abc|123|null # not allowed > > abc|456|null > > abc|456|987 > > abc|456|876 > > def|456|null > > def|456|null # not allowed > > > > Currently, the 'not allowed' lines are allowed. > > That is how 'unique' constraints are supposed to > work. One possible > solution is to use some normal value instead of > 'NULL' to represent > that fact. > I know ;). 'c' is actually 'parent_id' with a f/k contraint, so something like '0' wouldn't work. Hmm, IIRC indexes can have WHERE clauses - perhaps I can create a unique index that way... csn __________________________________________ Yahoo! DSL ? Something to write home about. Just $16.99/mo. or less. dsl.yahoo.com
