Re: Deferred partial/expression unique constraints

On Tuesday, July 12, 2011 08:57:44 PM Dean Rasheed wrote:
> On 12 July 2011 19:26, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
> > On 7/12/11 9:46 AM, Andres Freund wrote:
> >> Hi,
> >>
> >> I guess $subject wasn't implemented because plain unique indexes aren't
> >> represented in pg_constraint and thus do not have a place to store
> >> information about being deferred?
> >> Other than that I do not see any special complications in implementing
> >> it?
> >
> > Um, I thought that deferrable unique constraints were a 9.0 feature, no?
>
> Yes, but there is no syntax to create a unique constraint on an
> expression, and hence to create a deferrable unique expression check.
>
> However, that doesn't seem like such a serious limitation, because the
> same functionality can be achieved using an exclusion constraint with
> the equality operator.
That doesn't solve the issue of a partial index, right? Also I find it that
intuitive to package a expression inside an operator (which needs to be
complicated enough not to be accidentally used and still be expressive...).
Especially if that expression involves more than one column (which isn't that
hard to imagine).

Thanks,

Andres