創(chuàng)建2張用戶表user、user2，表結(jié)構(gòu)相同，但user表使用InnoDB存儲引擎，而user2表則使用 MyISAM存儲引擎。
-- Table "user" DDL
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(50) DEFAULT NULL,
`email` varchar(100) DEFAULT NULL,
`age` tinyint(4) DEFAULT NULL,
`nickname` varchar(50) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `email` (`email`),
KEY `name` (`name`),
KEY `age` (`age`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- Table "user2" DDL
CREATE TABLE `user2` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(50) DEFAULT NULL,
`email` varchar(100) DEFAULT NULL,
`age` tinyint(4) DEFAULT NULL,
`nickname` varchar(50) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `email` (`email`),
KEY `name` (`name`),
KEY `age` (`age`)
) ENGINE=MyISAM AUTO_INCREMENT=131610 DEFAULT CHARSET=utf8;
分別插入10W條測試數(shù)據(jù)到表user & user2。
<?php
$example = array(
'@qq.com',
'@sina.com.cn',
'@163.com',
'@126.com',
'@gmail.com',
'@yahoo.com',
'@live.com',
'@msn.com',
'@cisco.com',
'@microsoft.com',
'@ibm.com',
'@apple.com');
$con = mysql_connect("localhost", "root", "your_mysql_password");
mysql_select_db("index_test", $con);
//添加10W測試數(shù)據(jù)到表 user & user2
for($i=0; $i<100000; $i++)
{
$temp = md5(uniqid());
$name = substr($temp, 0, 16);
$email = substr($temp, 8, 12).$example[array_rand($example, 1)];
$age = rand(18, 99);
$nickname = substr($temp, 16, 16);
mysql_query("INSERT INTO user(name,email,age,nickname) VALUES('$name','$email',$age,'$nickname')");
mysql_query("INSERT INTO user2(name,email,age,nickname) VALUES('$name','$email',$age,'$nickname')");
}
mysql_close($con);
echo 'success';
?>
對索引的使用分析
Explain Select * from user where id>100 /G;
圖1
Explain Select * from user2 where id>100 /G;
圖2
User 表中的數(shù)據(jù)和 User2 表中的數(shù)據(jù)是一樣的，索引結(jié)構(gòu)也是一樣的，只不過它們的存儲引擎不同。在圖1中，查詢用到了PRIMARY主鍵索引，而查詢優(yōu)化器預(yù)估的結(jié)果大概在65954行左右（實際是131513）；在圖2中，查詢卻沒有使用索引，而是全表掃描了，返回的預(yù)估結(jié)果在131608行（實際是131509）。
Explain Select * from user where id>100 and age>50 /G;
圖3
Explain Select * from user where id>100 and age=50 /G;
圖4
Explain Select * from user2 where id>100 and age>50 /G;
圖5
Explain Select * from user2 where id>100 and age=50 /G;
圖6
