Re: index suggestion for 7.4

Bruno Wolff III <bruno(at)wolff(dot)to> writes:
> Now that expressions can be used in indexes in 7.4 you can have multicolumn
> indexes that are ordered in different directions. However the planner
> doesn't seem to understand that order by -col asc is the same as order by
> col desc (for at least the normal -)

I don't think it should; that's an extremely datatype-dependent bit of
analysis, and the planner does not have any means of ascertaining
whether the equivalency holds for a particular "-" operator and index
opclass.

The correct way to set up this sort of thing would be to build a
"backwards ordering" operator class, not to use an index on "-col".

regards, tom lane