Dean Rasheed <dean.a.rasheed@gmail.com> writes:
>>> On 7/12/11 9:46 AM, Andres Freund wrote:
>>>> 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?
> I agree that expressing that using a UNIQUE constraint would perhaps
> be more intuitive, but it would be new non-SQL-spec syntax that AFAICS
> wouldn't actually add any new functionality.
Our standard reason for not implementing UNIQUE constraints on
expressions has been that then you would have a thing that claims to be
a UNIQUE constraint but isn't representable in the information_schema
views that are supposed to show UNIQUE constraints. We avoid this
objection in the current design by shoving all that functionality into
EXCLUDE constraints, which are clearly outside the scope of the spec.
regards, tom lane