Re: [HACKERS] Re: [COMMITTERS] pgsql/src/include/parser (parse_node.h parse_oper.h)

Thomas Lockhart <lockhart@alumni.caltech.edu> writes:
>> Remove bogus code in oper_exact --- if it didn't find an exact
>> match then it tried for a self-commutative operator with the reversed input
>> data types.  This is pretty silly;

> Ooh! That codes sounds familiar. What I was trying for was to cover
> the case that, for example, (int4 < float4) was not implemented, but
> that (float4 >= int4) was. If this is already handled elsewhere, or if
> this goal is nonsensical, then cutting the defective code is the right
> thing. But if the code just needed repairing, we should put it back in
> and get it right next time...

Well, what it was actually looking for was not a commuted operator but
the *same* operator name with the reversed data types; and then
demanding that this operator link to itself as its own commutator.
I don't believe such a case can ever arise in practice --- it certainly
does not now, since the opr_sanity regress test would complain if it
did.

I don't see any really good way for operator lookup to substitute
commutative operators, since it has only an operator name and not (yet)
any pg_operator entry to check the commutator link of.  Surely you don't
want to hardwire in knowledge that, say, '<' and '>=' are likely to be
names of commutators.

In any case, failing to provide a full set of commutable comparison
operators will hobble the optimizer, so an implementor of a new data
type would be pretty foolish not to provide both operators.  So I don't
think it's worth providing code in operator lookup to handle this
scenario.
        regards, tom lane