Peter Eisentraut <peter_e@gmx.net> writes:
> On fre, 2010-11-12 at 09:44 -0500, Tom Lane wrote:
>> But I'm still not convinced that this feature is useful enough to
>> justify the implementation effort. AFAICS there's nothing here that
>> you couldn't get with some non-default operators on regular arrays,
> Unique constraints would behave differently for arrays and multisets.
> But I suppose you could get something similar with exclusion constraints
> nowadays. But not for primary keys.
> Foreign keys also don't work easily with nondefault operators.
> JOIN / USING doesn't work.
> ORDER BY would work but look ugly. And such coding where you'd have to
> remember the nondefault operator everywhere would also be error prone.
Hmm. Those are perhaps good arguments --- but you can't get any of
those behaviors unless multisets are distinct types. The implementation
proposed upthread where they're arrays with a special typmod isn't going
to support this.
regards, tom lane