mysql - 在大数据库中优化 SQL 查询？

Question

查询

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

MySQL 返回:

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

如果我删除 ORDER BY id DESC

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

解释计划:

计数

SELECT count( * )
FROM user_ip_tmp

使用的数据库示例

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 ;

我想要正确的方法来为 ORDER BY id DESC 查询和优化数据库

Answer 1

了解有关数据分布的一些信息会很有趣。您能否将以下查询的结果添加到您的帖子中？ (不需要图片，纯文本即可)。

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/'; 

此外，您能否测试此替代方案的性能？ 编辑:子查询的别名

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

编辑 如果添加和试验索引是一个选项，那么您可以尝试其中之一(或同时尝试两者，看看哪个更好)

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