As I know, IN sometimes invoke unmormal index. On Thu, May 28, 2009 at 1:15 AM, Baron Schwartz <ba...@xaprb.com> wrote:
> Simon, > > On Wed, May 27, 2009 at 11:23 AM, Simon J Mudd <sjm...@pobox.com> wrote: > > per...@elem.com (Perrin Harkins) writes: > > > >> On Wed, May 27, 2009 at 6:43 AM, Simon J Mudd <sjm...@pobox.com> wrote: > >> > So is the format of the DELETE FROM .. WHERE ... IN ( ... ) clause I > >> > propose valid and SHOULD the optimiser recognise this and be expected > >> > to just find the 2 rows by searching on the primary key? > >> > >> Not according to the docs: > >> > http://dev.mysql.com/doc/refman/5.1/en/comparison-operators.html#function_in > > > > I'm not sure that the reference makes anything clear. The statements > > are wrote ARE valid SQL and even though containing mulitiple column > > values ARE "constants". > > > > Problem is I'm finding it hard to find a definitive reference to > something > > like this. I'll have to check my Joe Celko books to see if he mentions > ths. > > Nothing's wrong with the SQL -- it's just that MySQL doesn't optimize > this type of query well. > > See > http://code.openark.org/blog/mysql/mysql-not-being-able-to-utilize-a-compound-index > > Regards > Baron > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/mysql?unsub=yueliangdao0...@gmail.com > > -- David Yeung, MySQL Senior Support Engineer, Sun Gold Partner. My Blog:http://yueliangdao0608.cublog.cn Comanpy: http://www.actionsky.com
