On 12/15/2011 03:53 PM, Alban Hertroys wrote:
> Correct, but...
> That's not a particularly useful index to create. That index just contains values of true where the associated column equals true - you're storing the same information twice.
It could be very handy if you have an extremely high selectivity index
(say 1:1000 or more) where you want to keep the index tiny, fast, and
very quick to scan.
I guess ideally Pg would be able to deduce that the index value is
always the same and just store a page list rather than a b-tree, but
it's a bit of a tiny use case.
--
Craig Ringer