Re: Using unique btree indexes for pathkeys with one extra column

Thomas Munro <thomas.munro@gmail.com> writes:
> In the category "doing more tricks with our existing btrees", which
> includes all that difficult stuff like skip scans and incremental
> sort, here's an easier planner-only one:  if you have a unique index
> on (a) possibly "including" (b) and you have a pathkey (a, b), you can
> use an index [only] scan.  That is, if the index is unique, and you
> want exactly one extra column in index order, then you don't need any
> extra sorting to get (a, b) in order.  (If the index is not unique, or
> there is more than one extra trailing column in the pathkey, you need
> the incremental sort patch[1] to use this index).

Seems like you also have to insist that a is NOT NULL.

            regards, tom lane