>>>>> "Tom" == Tom Lane <tgl@sss.pgh.pa.us> writes:
> Andrew Gierth <andrew@tao11.riddles.org.uk> writes:
>> Type-dependent selection of operators has already been done as
>> part of parse analysis, no? And the domain -> base conversion is
>> purely a relabelling, no? So what semantic change is possible as a
>> result?
Tom> Domain conversions are *not* simply relabellings. It's possible
Tom> now to have domain-specific functions/operators,
Right, but that's irrelevent to the planner in this case because the
resolution of precisely which operator is being called has _already
happened_ (in parse analysis), no?
Tom> It's possible that there are specific cases where the UNION
Tom> optimization checks could allow domains to be treated as their
Tom> base types,
The domain -> base conversion is an important one (to anyone who uses
domains) because it happens implicitly in a wide range of contexts,
and so it's unsatisfactory for it to have major performance impacts
such as interfering with important optimizations.
Tom> but blindly smashing both sides of the check to base is going to
Tom> break more cases than it fixes.
The posted code was only looking up the base type for one side, not
both (though I don't know that code well enough to know whether it was
the correct side); the case of interest is when the subquery has the
domain type but the outer query is seeing the base type, _not_ the
reverse.
--
Andrew.
