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mysql索引

2022-08-05 09:34:00 【51CTO】

1 索引的创建

1.1 普通索引

mysql索引_mysql索引的创建

mysql索引_主键_02

1.2 .唯一索引

       
       mysql> create UNIQUE index index_unique on user1(username);
       
mysql> show create table user1\G; 
       
       Table: user1
       
Create Table: CREATE TABLE `user1` (
       
  `id` int(11) DEFAULT NULL,
       
  `username` char(10) DEFAULT NULL,
       
  `password` varchar(20) DEFAULTNULL,
       
  `address` varchar(20) DEFAULTNULL,
       
  UNIQUE KEY `index_unique`(`username`)
       
) ENGINE=InnoDB DEFAULT CHARSET=gbk
       
1 row in set (0.00 sec)
       
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1. 3 .主键索引

       
       mysql>  alter table user1 addprimary key(id);
       
Query OK, 2 rows affected (0.16 sec)
       
Records: 2  Duplicates: 0  Warnings: 0
       
mysql> show create table user1\G;
       
      Table: user1
       
Create Table: CREATE TABLE `user1` (
       
  `id` int(11) NOT NULL DEFAULT '0',
       
  `username` char(10) DEFAULT NULL,
       
  `password` varchar(20) DEFAULTNULL,
       
  `address` varchar(20) DEFAULTNULL,
       
  PRIMARY KEY (`id`),
       
  UNIQUE KEY `index_unique`(`username`)
       
) ENGINE=InnoDB DEFAULT CHARSET=gbk
       
1 row in set (0.00 sec)
      
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2 索引删除

删除唯一索引

mysql>alter table user1 drop index index_unique;

删除主键索引

第一种方法：

mysql> alter table user1 drop index primary key;

第二种方法：

mysql> drop index index_name on users;

3 复合索引

       
       mysql> alter table user1 add index index_address_age(address,age);
       
Query OK, 0 rows affected (0.21 sec) 
       
mysql> show create table user1\G;
       
Table: user1
       
Create Table: CREATE TABLE `user1` (
       
  `id` int(11) NOT NULL DEFAULT '0',
       
  `username` char(10) DEFAULT NULL,
       
  `password` varchar(20) DEFAULTNULL,
       
  `address` varchar(20) DEFAULTNULL,
       
  `age` int(11) DEFAULT NULL,
       
  KEY `index_address_age`(`address`,`age`)
       
) ENGINE=InnoDB DEFAULT CHARSET=gbk
       
1 row in set (0.00 sec)
       
mysql>
      
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