On Tue, 2007-11-06 at 08:01 -0500, Mark Mielke wrote:
> Simon Riggs wrote:
> > On Mon, 2007-11-05 at 09:52 +0000, Heikki Linnakangas wrote:
> > I'm racking my brain trying to think of a query that will benefit from
> > index-only scans without specifically creating covered indexes. Apart
> > from count(*) queries and RI lookups. I can't see RI lookups being much
> > cheaper with this technique, do you see something there
> I'm not sure what RI lookup is. Sorry. :-)
>
> My list would be:
> - EXISTS / NOT EXISTS
> - COUNT(*)
> - Tables that are heavily updated - any case where the index entry often
> maps to a non-visible tuple.
>
> Beyond that, yeah, I cannot think of other benefits.
>
What about range queries or sorts?
The correlation of an index to itself is 100% :)
Regards,
Jeff Davis
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
