| From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
|---|---|
| To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgreSQL(dot)org |
| Subject: | Re: Simplifying pg_am representation of index sortability |
| Date: | 2007-01-21 11:17:31 |
| Message-ID: | 20070121111731.GA2123@svana.org |
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| Lists: | pgsql-hackers |
On Sun, Jan 21, 2007 at 09:39:32AM +0000, Gregory Stark wrote:
> I guess it's tricky since there may be operators which have valid negators and
> commutators but which don't get used by any btree operator class. Does
> Postgres actually make use of the oprcom and oprnegate in that case? Could
> they be used only for such operators to provide values for when they can't be
> automatically deduced?
Sure, they're used whenever you have expressions of the form (CONST OP
VAR) or NOT(VAR OP CONST). This is basic expression simplification that
has little to do with b-trees in general.
You have operators like "contains" and "is contained by" which would be
opposites of eachother, but could never be used in a b-tree class.
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.
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