Hi, On 2018-12-05 13:22:23 -0500, Tom Lane wrote: > Andres Freund <and...@anarazel.de> writes: > > On 2018-12-05 12:24:54 -0500, Tom Lane wrote: > >> There are two different issues in that. One is that the domain might > >> have constraints (though in reality it does not), so the planner can't > >> throw away the CoerceToDomain node, and thus can't match the expression > >> to the index. Even if we did throw away the CoerceToDomain, it still > >> would not work because the domain is declared to be over varchar, and > >> so there's a cast-to-varchar underneath the CoerceToDomain. > > > Couldn't we make expression simplification replace CoerceToDomain with a > > RelabelType if the constraint is simple enough? That's not entirely > > trivial because we'd have to look into the typecache to get the > > constraints, but that doesn't sound too bad. > > Not following what you have in mind here? My 0002 throws away the > CoerceToDomain if there are *no* constraints, but I can't see any > situation in which we'd likely be able to ignore a constraint, > simple or not.
Yea, simple probably means nonexistant for now. We could e.g. optimize some NOT NULL checks away, but it's probably not worth it. > >> 0003 essentially converts "namecol::text texteq textvalue" into > >> "namecol nameeqtext textvalue", relying on the new equality > >> operator introduced by 0001. > > > Ugh, that's indeed a bit kludgy. It'd be nice to have an approach that's > > usable outside of one odd builtin type. I was wondering for a bit > > whether we could have logic to move the cast to the other side of an > > operator, but I don't see how we could make that generally safe. > > Yeah. It seems like it could be a special case of a more general > expression transform facility, but we have no such facility now. > > On the other hand, all of match_special_index_operator is an ugly > single-purpose kluge already, so I'm not feeling that awful about > throwing another special case into it. Someday it would be nice > to replace that code with something more general and extensible, > but today is not that day as far as I'm concerned. Fair enough. Greetings, Andres Freund
