一、创建索引
1、 创建表的时候创建索引
mysql> create table student(
-> id bigint(20) not null auto_increment,
-> name char(20) not null,
-> age tinyint(3) not null default '0',
-> dept varchar(30) not null,
-> primary key(id), -- 主键索引
-> key idx_name(name)); -- 普通索引
2、创建索引方式一
2.1 语法
普通索引 ： alter table <表名> add index <索引名称>(<字段名称>);
唯一索引 ： alter table <表名> add unique index <索引名称>(<字段名称>);
普通组合索引： alter table <表名> add index<索引名称>(<字段名称>,<字段名称>,...);
唯一组合索引： alter table <表名> add unique index<索引名称>(<字段名称>,<字段名称>,...);
2.2 案例
mysql> desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | | NULL | |
| age | tinyint(3) | NO | | 0 | |
| dept | varchar(30) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> alter table student add index idx_name(name);
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc
-> student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | MUL | NULL | |
| age | tinyint(3) | NO | | 0 | |
| dept | varchar(30) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
3、创建索引方式二：
3.1 语法
普通索引： create index <索引名称> on <表名>(<表中字段>);
唯一索引： create unique index <索引名称> on <表名>(<表中字段>);
普通组合索引： create index <索引名称> on <表名>(<表中字段>,<字段名称>,...);
唯一组合索引： create unique index <索引名称> on <表名>(<表中字段>,<字段名称>,...);
3.2 案例
mysql> desc
-> student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | MUL | NULL | |
| age | tinyint(3) | NO | | 0 | |
| dept | varchar(30) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> create index idx_dept on student(dept);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | MUL | NULL | |
| age | tinyint(3) | NO | | 0 | |
| dept | varchar(30) | NO | MUL | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
二、查看索引
1、方式一：desc <表名>
mysql> desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | MUL | NULL | |
| age | tinyint(3) | NO | | 0 | |
| dept | varchar(30) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
PRI ：主键索引标识，MUL：普通索引标识，UNI：唯一索引标识
2、 方式二：show index from <表名>
mysql> show index from student \G;
*************************** 1. row ***************************
Table: student
Non_unique: 0
Key_name: PRIMARY
Seq_in_index: 1
Column_name: id
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
*************************** 2. row ***************************
Table: student
Non_unique: 1
Key_name: idx_name
Seq_in_index: 1
Column_name: name
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
*************************** 3. row ***************************
Table: student
Non_unique: 1
Key_name: idx_dept
Seq_in_index: 1
Column_name: dept
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
3 rows in set (0.00 sec)
三、删除索引
1、方式一：alter table <表名> drop index <索引名称>
1.1 语法
alter table <表名> drop index <索引名称>;
1.2 案例
mysql> desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | MUL | NULL | |
| age | tinyint(3) | NO | | 0 | |
| dept | varchar(30) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> alter table student drop index idx_name;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | | NULL | |
| age | tinyint(3) | NO | | 0 | |
| dept | varchar(30) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
2、方式二:drop index <索引名称> on <表名>
2.1 案例
mysql> drop index idx_name_dept on student;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
