mysql索引

索引

索引

推荐博客MySQL索引原理以及查询优化

创建表

CREATE TABLE emp(
id INT ,
NAME VARCHAR(20),
gender VARCHAR(10),
email VARCHAR(50)
);

插入数据

临时增加插入效率

mysql> set  autocommit  =off;
mysql> show variables like 'autocom%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit    | OFF   |
+---------------+-------+
1 row in set (0.00 sec)

存储过程快速插入

delimiter $$
create procedure auto_insert1()
BEGIN
    declare i int default 1;
    while(i<3000000)do
         insert into emp values(i,concat('jack',i),'male',concat('www.jack',i,'@qq.com'));
        set i=i+1;
    end while;
END$$
delimiter ; 

调用call auto_insert1()
手动 commit;

插入操作

mysql> delimiter $$
mysql> create procedure auto_insert1()
    -> BEGIN
    ->     declare i int default 1;
    ->     while(i<300000)do
    ->         insert into employer values(i,concat('egon',i),'male',concat('egon',i,'@oldboy'));
    ->         set i=i+1;
    ->     end while;
    -> END$$
Query OK, 0 rows affected (0.04 sec)

mysql> delimiter ;
mysql> show create procedure  auto_insert1 G
*************************** 1. row ***************************
           Procedure: auto_insert1
            sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
    Create Procedure: CREATE DEFINER=`root`@`%` PROCEDURE `auto_insert1`()
BEGIN
    declare i int default 1;
    while(i<300000)do
insert into employer values(i,concat('jack',i),'male',concat('www.jack',i,'@qq.com'));
        set i=i+1;
    end while;
END
character_set_client: latin1
collation_connection: latin1_swedish_ci
  Database Collation: utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

mysql> call auto_insert1();
Query OK, 1 row affected (5 min 50.89 sec)
mysql> drop PROCEDURE auto_insert1;
mysql> commit;
Query OK, 0 rows affected (10.24 sec)
mysql> exit;

不增加索引查询耗时

耗时4s

mysql> select * from emp where id = 33333;
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 33333 | jack33333 | male   | www.jack33333@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (4.55 sec)

存在300万数据的时候增加索引耗时

mysql> create index indexid on emp(id);
Query OK, 0 rows affected (21.24 sec)
Records: 0  Duplicates: 0  Warnings: 0

增加索引的查询耗时

mysql> select * from emp where id = 33333;
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 33333 | jack33333 | male   | www.jack33333@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (0.00 sec)

mysql> select * from emp where id = 100333;
+--------+------------+--------+-----------------------+
| id     | NAME       | gender | email                 |
+--------+------------+--------+-----------------------+
| 100333 | jack100333 | male   | www.jack100333@qq.com |
+--------+------------+--------+-----------------------+
1 row in set (0.01 sec)

删除主键

mysql> select * from emp where id =10000;
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 10000 | jack10000 | male   | www.jack10000@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (0.00 sec)

mysql> drop index indexid on emp;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from emp where id =10001;
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 10001 | jack10001 | male   | www.jack10001@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (4.79 sec)

mysql> help create index^C
mysql> create index indexid on emp(id);
Query OK, 0 rows affected (19.61 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from emp where id =20001;
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 20001 | jack20001 | male   | www.jack20001@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (0.00 sec)

mysql>

创建索引的语法

1.创建索引
    -在创建表时就创建（需要注意的几点）
    create table s1(
    id int ,#可以在这加primary key
    #id int index #不可以这样加索引，因为index只是索引，没有约束一说，
    #不能像主键，还有唯一约束一样，在定义字段的时候加索引
    name char(20),
    age int,
    email varchar(30)
    #primary key(id) #也可以在这加
    index(id) #可以这样加
    );
    -在创建表后在创建
    create index name on s1(name); #添加普通索引
    create unique age on s1(age);添加唯一索引
    alter table s1 add primary key(id); #添加住建索引，也就是给id字段增加一个主键约束
    create index name on s1(id,name); #添加普通联合索引
2.删除索引
    drop index id on s1;
    drop index name on s1; #删除普通索引
    drop index age on s1; #删除唯一索引，就和普通索引一样，不用在index前加unique来删，直接就可以删了
    alter table s1 drop primary key; #删除主键(因为它添加的时候是按照alter来增加的，那么我们也用alter来删)

组合索引

创建组合索引

mysql> create index indexidname  on emp(id,name);
Query OK, 0 rows affected (30.87 sec)

组合索引可以命中的查询语句

mysql> select * from emp where id=10000 and name ='jack10000';
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 10000 | jack10000 | male   | www.jack10000@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (0.00 sec)

从左到右原则不会命中下面的查询语句
mysql> select * from emp where name ='jack10000';
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 10000 | jack10000 | male   | www.jack10000@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (5.48 sec)

mysql> select * from emp where id =10000;
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 10000 | jack10000 | male   | www.jack10000@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (0.00 sec)

查询优化

索引是为了增加查询的效率，查询需要注意：

1. 避免使用select 、count*这样的操作

mysql> select name  from emp where name ='jack10000';
+-----------+
| name      |
+-----------+
| jack10000 |
+-----------+
1 row in set (4.15 sec)

mysql> select *  from emp where name ='jack10000';
+-------+-----------+--------+----------------------+
| id    | NAME      | gender | email                |
+-------+-----------+--------+----------------------+
| 10000 | jack10000 | male   | www.jack10000@qq.com |
+-------+-----------+--------+----------------------+
1 row in set (5.48 sec)

mysql> select count(1) from emp;
+----------+
| count(1) |
+----------+
|  2999999 |
+----------+
1 row in set (2.47 sec)

mysql> select count(*) from emp;
+----------+
| count(*) |
+----------+
|  2999999 |
+----------+
1 row in set (2.72 sec)

2. 索引尽量短
3. 查询条件复杂使用联合索引