performance difference between UNION operator and OR in where clause Options
Date: Wed, 11 Jul 2007 06:21:45 -0700
purpose: find all publication titles for books or journals.
precondition: both book and journal tables are not empty. (if either is empty, the following solution 2 will be wrong. See my old post "difference between UNION operator and OR in where clause Options" for details).
Solution 1: use set "union"
from publication, ( (select pubid from book) UNION (select pubid from journal)) bj
where publication.pubid = bj.pubid
solution 2: use "or" operator in the where clause
select DISTINCE title
from publication, book, journal
where publication.pubid = book.pubid or publication.pubid = journal.pubid
Both solutions are correct under the precondition.
My question is which one should use for better performance ?
My intuitive guess will be solution 2.
Any comments ?
Thanks ahead. Received on Wed Jul 11 2007 - 15:21:45 CEST