At 11:18 AM 17-05-2000 -0400, Tom Lane wrote:
>In fact, IN (subselect), INTERSECT, and EXCEPT are all pretty much the
>same thing, and they're all pretty slow in the current code :-(, because
>they all work by rescanning the inner query for each outer tuple --- in
>other words, they're all implemented like plain nestloop joins. EXISTS
>is marginally better because the planner can figure out how to use an
>index on the inner table, if there is one.
Does that mean for two tables, one 1000 rows another 2000 rows, it's a
total of 1000 X 2000 rows scanned?
I suppose one way to slightly reduce the number of rows would be to select
stuff into temp tables first.
Cheerio,
Link.