Interesting, but that assumes there's a value to use in the coalesce that isn't a valid data value.
__________________________________________________________________________________ *Mike Blackwell | Technical Analyst, Distribution Services/Rollout Management | RR Donnelley* 1750 Wallace Ave | St Charles, IL 60174-3401 Office: 630.313.7818 mike.blackw...@rrd.com http://www.rrdonnelley.com <http://www.rrdonnelley.com/> * <mike.blackw...@rrd.com>* On Tue, Sep 25, 2012 at 10:32 AM, hubert depesz lubaczewski < dep...@depesz.com> wrote: > On Tue, Sep 25, 2012 at 10:05:15AM -0500, Mike Blackwell wrote: > > How would one go about building a multi-column unique constraint where > null > > is a significant value, eg. (1, NULL) <> (2, NULL)? > > > > I see a number of references to not being able to use an index for this, > > but no mention of an alternative. Any pointers would be appreciated > > create unique index zzz on table ((column is null), coalesce(column, > 'whatever')); > > Best regards, > > depesz > > -- > The best thing about modern society is how easy it is to avoid contact > with it. > > http://depesz.com/ >
