例如这样一个表,我想统计email和passwords都不相同的记录的条数
CREATE TABLE IF NOT EXISTS `test_users` (
`email_id` int(11) unsigned NOT NULL auto_increment,
`email` char(100) NOT NULL,
`passwords` char(64) NOT NULL,
PRIMARY KEY (`email_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=6 ;
INSERT INTO `test_users` (`email_id`, `email`, `passwords`) VALUES
(1, ‘jims@gmail.com', ‘1e48c4420b7073bc11916c6c1de226bb'),
(2, ‘jims@yahoo.com.cn', ‘5294cef9f1bf1858ce9d7fdb62240546′),
(3, ‘default@gmail.com', ‘5294cef9f1bf1858ce9d7fdb62240546′),
(4, ‘jims@gmail.com', ”),
(5, ‘jims@gmail.com', ”);
通常我们的做法是这样
SELECT COUNT(*) FROM test_users WHERE 1 = 1 GROUP BY email,passwords
这样的结果是什么呢?
COUNT(*)
1
2
1
1
显然这不是我要的结果,这样统计出来的是相同email和passwords的各个记录数量之和,下面这样就可以了
SELECT COUNT(DISTINCT email,passwords) FROM `test_users` WHERE 1 = 1
当然在php里面也可以用mysql_num_rows来获取记录的条数,但是这样的效率不高,可以参考这篇文章
mysql_num_rows VS COUNT 效率问题分析

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