Greg Stark <gsstark@mit.edu> writes:
> The thing is that these opclasses you're describing are closely related. It
> ought to be possible to use a single index to produce results in any of the
> four orders you describe.
Wrong --- only two of them. You can't magically swap nulls from one end
of the index to the other (and Hannu's flight of fantasy about double
indexscans is just a flight of fantasy; it would be solving the problem
at entirely the wrong place).
> These aren't all related in the same way.
They are all desirable properties of an index column, however. In
particular, we do have a market for genuine reverse-sort columns,
so that you can use a double-column index to get orderings like
ORDER BY x ASC, y DESC.
regards, tom lane
