Marko Tiikkaja <marko.tiikk...@cs.helsinki.fi> wrote: > On 5/21/10 11:47 PM +0300, Jeff Davis wrote: > > It also allows you to enforce the constraint that only one tuple exists > > in a table by doing something like: > > > > create table a > > ( > > i int, > > exclude using gist (i with<>), > > unique (i) > > );
+1. I've not read the code, but it might be considerable that we can abort index scans if we find a first index entry for "i". While we must scan all candidates for "WHERE i <> ?", but we can abort for the constraint case because we know existing values are all the same. > FWIW, this is achievable a lot more easily: > CREATE UNIQUE INDEX "a_single_row" ON a ((1)); The former exclusion constraint means "one same value for all rows", but your alternative means "a_single_row", right? Regards, --- Takahiro Itagaki NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
