MySQL索引應用全程剖析。本站提示廣大學習愛好者:(MySQL索引應用全程剖析)文章只能為提供參考,不一定能成為您想要的結果。以下是MySQL索引應用全程剖析正文
創立2張用戶表user、user2,表構造雷同,但user表應用InnoDB存儲引擎,而user2表則應用 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;
分離拔出10W條測試數據到表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", $con);
//添加10W測試數據到表 user & user2
for($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';
?>
對索引的應用剖析
Explain Select * from user where id>100 \G;
圖1
Explain Select * from user2 where id>100 \G;
圖2
User 表中的數據和 User2 表中的數據是一樣的,索引構造也是一樣的,只不外它們的存儲引擎分歧。在圖1中,查詢用到了PRIMARY主鍵索引,而查詢優化器預估的成果年夜概在65954行閣下(現實是131513);在圖2中,查詢卻沒有應用索引,而是全表掃描了,前往的預估成果在131608行(現實是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