On Tue, Mar 8, 2011 at 3:21 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Not so right. A path key contains an expression tree, plus whatever > *additional* information is needed to fully specify the sort ordering. > If the collation is already fully determined by the expression tree, > there is no need to duplicate that information in the PathKey node. > And, as I said, doing so anyway has real negative consequences.
Isn't the reason to copy that information outside the expression so that we can choose sometimes to ignore it? Namely, for == we can use an index with any defined collation even if it doesn't match the collation in the pathkey we're looking for? I think currently that's the only example but in theory we could have collations that are "supersets" of the desired collation. For example a UTF8 collation that sorts english in the desired way and sorts utf8 characters in some way that isn't relevant to the query. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
