Jan Urbański <j.urbanski@students.mimuw.edu.pl> writes:
> All three try to sort the table first, and as there's no comparision
> operator for the POINT datatype, they fail. Which seems to be wrong - if
> there is no comparision operator, you still can do DISTINCT, only less
> efficiently.
Type point has no btree opclass, no hash opclass, and not even an
operator named "=" (it looks like the functionality is named ~=
for some odd reason). I'd be interested to hear either a proposal of
a principled way to define DISTINCT, or a way to implement it that
was better than comparing every element to every other element...
regards, tom lane