在大型数据库中优化SQL查询？

Question

Query

SELECT *
FROM user_ip_tmp
WHERE too = 'http://example.com/'
AND contry != 'CN'
AND contry != 'TW'
ORDER BY id DESC
LIMIT 50 

MySQL returns:

Showing rows 0 - 29 ( 50 total, Query took 11.9276 sec) [id: 3452538 - 3448824]

if i remove ORDER BY id DESC

Showing rows 0 - 29 ( 50 total, Query took 0.0033 sec)

Explain plan:

count

SELECT count( * )
FROM user_ip_tmp

Example of the database used

CREATE TABLE IF NOT EXISTS `user_ip_tmp` (
  `id` int(9) NOT NULL AUTO_INCREMENT,
  `ip` varchar(20) NOT NULL,
  `dataip` bigint(20) NOT NULL,
  `ref` text NOT NULL,
  `click` int(20) NOT NULL,
  `code` varchar(17) NOT NULL,
  `too` text NOT NULL,
  `checkopen` varchar(17) NOT NULL,
  `contry` text NOT NULL,
  `vOperation` text NOT NULL,
  `vBrowser` text NOT NULL,
  `iconOperation` text NOT NULL,
  `iconBrowser` text NOT NULL,
  PRIMARY KEY (`id`),
  KEY `ip` (`dataip`),
  KEY `ip` (`checkopen`),
  KEY `ip` (`code`),
  KEY `ip` (`too`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=5426268 ;

I want the correct way to do the query and optimize database for ORDER BY id DESC

Answer 1

It would be interesting to know something about the distribution of your data. Could you add the results of the following queries to your post? (no need for pictures, plain text will do).

SELECT count(*) FROM user_ip_tmp WHERE too = 'http://example.com/' AND contry != 'CN' AND contry != 'TW'; 

SELECT count(*) FROM user_ip_tmp WHERE too = 'http://example.com/'; 

Also, could you test this alternative for performance? EDIT: alias for subquery

SELECT sub.* FROM
(SELECT *
FROM user_ip_tmp
WHERE too = 'http://example.com/'
AND contry != 'CN'
AND contry != 'TW'
) sub
ORDER BY sub.id DESC
LIMIT 50

Edit If it is an option to add and experiment with indexes, then you could try one of these (or both and see which is better)

CREATE INDEX index_name ON `user_ip_tmp` (`too`, `id`);
CREATE INDEX index_name ON `user_ip_tmp` (`too`, `contry`, `id`);

Answer 2

您可以使用以下方法创建索引：

 id, too and contry