Hi Simon, once you apply functions to a field, an index on that field is pretty much useless. For this particular query, I would be tempted to create additional fields to store the values of MONTH(articles.created_at) and DAY(articles.created_at). Create an index on (month_created, day_created) You could just sort by articles.created_at; no need for the YEAR function, the result will be the same given your other selectors.
Given those adjustments, the query looks righteous enough. - michael dykman On Tue, Jan 18, 2011 at 12:22 PM, Simon Wilkinson <simon.wilkin...@gmail.com> wrote: > Hi, > > I am trying to optimize the following query: > > SELECT articles.* FROM articles INNER JOIN newsletters ON > articles.newsletter_id = newsletters.id INNER JOIN users ON users.id = > newsletters.user_id WHERE users.id =12 AND MONTH(articles.created_at) = '12' > AND DAY(articles.created_at) = '5' ORDER BY YEAR(articles.created_at), > LENGTH(articles.body); > > I am trying to retrieve all the articles created on a specific day of a > specific month that belong to a user, ordered by the oldest and then longest > article. > > I have run explain on the query, and get the following: > > +----+-------------+----------+-------+------------------------------------------------------------------------+--------------------------------------------+---------+---------------------+------+----------------------------------------------+ > | id | select_type | table | type | > possible_keys | > key | key_len | ref | > rows | Extra | > +----+-------------+----------+-------+------------------------------------------------------------------------+--------------------------------------------+---------+---------------------+------+----------------------------------------------+ > | 1 | SIMPLE | users | const | > PRIMARY | > PRIMARY | 4 | const > | 1 | Using index; Using temporary; Using filesort | > | 1 | SIMPLE | newsletters | ref | > PRIMARY,index_newsletters_on_user_id | > index_newsletters_on_user_id | 4 | > const | 1 | Using index | > | 1 | SIMPLE | articles | ref | > index_articles_on_newsletter_id,index_articles_on_newsletter_id_and_created_at > | index_articles_on_newsletter_id_and_created_at | 4 | > my_db.newsletters.id | 3 | Using where | > > +----+-------------+----------+-------+------------------------------------------------------------------------+--------------------------------------------+---------+---------------------+------+----------------------------------------------+ > 3 rows in set (0.00 sec) > > This seems pretty decent, and does perform pretty well for some users (~0.5 > - 1 sec), but for some users (seemingly those with large numbers of > articles) the query can take 20 - 30 seconds to run. This seems really slow > to me. I tried adding in the index > 'index_articles_on_newsletter_id_and_created_at' but the performance doesn't > seem to be any different then when it uses just the > 'index_articles_on_newsletter_id' index. I think this might be because of > the functions I am using on the created_at column to get the day and month > from it, making an index on created_at useless in this instance. > > Running both an 'optimize table entries' and 'analyze table entries' also > didn't seem to have any real impact on the performance. > > I was wondering if anybody had any suggestions for what else I might be able > to try, or if there is a better way to search on dates in this manner. Any > ideas would be greatly appreciated. > > Thanks, > > Simon > -- - michael dykman - mdyk...@gmail.com May the Source be with you. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
