Andrew - Supernews <andrew+nonews(at)supernews(dot)com> writes:
> You're suffering from a fundamental confusion between the ltcmp/rtcmp
> operators (which indeed must be trichotomous with the join operator)
> and the sort operators.
[ thinks for awhile... ] OK, you have a point, but if we want to take
that seriously then we have to invent a different concept that supports
what the planner needs to do, ie, draw transitive-equality inferences
("if A = B and B = C then A = C").
The real question on the table is whether it's worth distinguishing
between mergejoinable equality operators and transitive equality
operators. I suggest that it probably isn't --- do you have any
examples with more real-world application than the x = 2y case?
regards, tom lane