Re: UNION or OR / INTERSECT or AND ?

On Feb 7, 2006, at 23:04 , David W wrote:

> do i have to prefered to use UNION and INTERSECT or is it better with
> OR and AND ?

In general, EXPLAIN ANALYZE is your friend. I suspect using OR will
be better (and that's only a suspicion), but by using EXPLAIN ANALYZE
you can see exactly how the server is planning the queries based on
your actual situation (as long as your statistics are accurate. See
ANALYZE as well).

[EXPLAIN](http://www.postgresql.org/docs/current/interactive/sql-
explain.html)
[ANALYZE](http://www.postgresql.org/docs/current/interactive/sql-
analyze.html)

Once you've got some good EXPLAIN ANALYZE output, people on the
performance list may be able to help out if you still have questions.

http://archives.postgresql.org/pgsql-performance/

Michael Glaesemann
grzm myrealbox com