MySQL Query Optimization - mysql

Question

I have web application that use a similar table scheme like below. simply I want to optimize the selection of articles. articles are selected based on the tag given. for example, if the tag is 'iphone' , the query should output all open articles about 'iphone' from the last month.
CREATE TABLE `article` (
`id` int(11) NOT NULL auto_increment,
`title` varchar(100) NOT NULL,
`body` varchar(200) NOT NULL,
`date` timestamp NOT NULL default CURRENT_TIMESTAMP,
`author_id` int(11) NOT NULL,
`section` varchar(30) NOT NULL,
`status` int(1) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;
CREATE TABLE `tags` (
`name` varchar(30) NOT NULL,
`article_id` int(11) NOT NULL,
PRIMARY KEY (`name`,`article_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
CREATE TABLE `users` (
`id` int(11) NOT NULL auto_increment,
`username` varchar(30) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=3 ;
The following is my MySQL query
explain select article.id,users.username,article.title
from article,users,tags
where article.id=tags.article_id and tags.name = 'iphone4'
and article.author_id=users.id and article.status = '1'
and article.section = 'mobile'
and article.date > '2010-02-07 13:25:46'
ORDER BY tags.article_id DESC
the output is
id select_type table type possible_keys key key_len ref rows Extra <br>
1 SIMPLE tags ref PRIMARY PRIMARY 92 const 55 Using where; Using index <br>
1 SIMPLE article eq_ref PRIMARY PRIMARY 4 test.tags.article_id 1 Using where <br>
1 SIMPLE users eq_ref PRIMARY PRIMARY 4 test.article.author_id 1 <br>
is it possible to optimize it more?

Answer 1

This query may be optimized, depending on which condition is more selective: tags.name = 'iphone4' or article.date > '2010-02-07 13:25:46'
If there are less articles tagged iphone than those posted after Feb 7, then your original query is nice.
If there are many articles tagged iphone, but few those posted after Feb 7, then this query will be more efficient:
SELECT article.id, users.username, article.title
FROM tags
JOIN article
ON article.id = tags.article_id
AND article.status = '1'
AND article.section = 'mobile'
AND article.date > '2010-02-07 13:25:46'
JOIN users
ON users.id = article.author_id
WHERE tags.name = 'iphone4'
ORDER BY
tags.article_date DESC, tags.article_id DESC
Note that the ORDER BY condition has changed. This may or may not be what you want, however, generally the orders of id and date correspond to each other.
If you really need your original ORDER BY condition you may leave it but it will add a filesort (or just revert to your original plan).
In either case, create an index on
article (status, section, date, id)

Answer 2

the query should output all open articles about 'iphone' from the last month.
So the only query you are going to run on this data uses the tag and the date. You've got a index for the tag in the tags table, but the date is stored in a different table (article - you're a bit inconsistent with your naming schema). Adding an index on the article table using date would be no benefit at all. Using id,date (in that order) would help a little - but really the date needs to be denormalised into the tags table to get the query running really fast.
Unless you're regularly moving around bulk data sets - just add a datetime column with a default of the current timestamp to the tags table.
I expect that you may be wanting to interact with the data in lots of other ways - really you should set a low (no?) threshold for slow query logging then analyse the resulting data to identify where you're performance problems are (try looking at the queries with the highest values for duration^2*frequency first).
There's a script at the URL below which is useful for this analysis:
http://www.retards.org/projects/mysql/

Answer 3

You could index the additional fields in article that you are referencing in your select statement. In this case, I would suggest you create an index in article like this:
CREATE INDEX article_idx ON article (author_id, status, section, date);
Creating that index should speed up your query depending on how many overall records you are dealing with. From my understanding, properly creating indexes involves looking at the queries you've written and indexing the columns that are a part of your where clause. This helps the query optimizer better process the query in general. That does not mean create an index on each individual column, however, as its both inefficient to do so and ineffective. When possible, create multiple column indexes that represent your select statement.