Mysql添加约束

MySQL中对三种约束的支持： http://leekai.me/mysql-zhong-dui-san-zhong-yue-shu-de-zhi-chi/
MySQL的InnoDB默认支持5中约束，
– primary key
– unique key
– foreign key
– default
– not null
今天我们来操作一下唯一约束创建与删除，首先创建表：

CREATE TABLE `user1` (
  `name` varchar(20) NOT NULL,
  `email` varchar(100) default NULL,
  `phone` varchar(11) default NULL,
  PRIMARY KEY  (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

查看表描述：

mysql> use test;
Database changed
mysql> desc user1;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| name  | varchar(20)  | NO   | PRI |         |       |
| email | varchar(100) | YES  |     | NULL    |       |
| phone | varchar(11)  | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set

添加唯一约束：

mysql> alter table user1 add constraint emailUnique UNIQUE(email);
Query OK, 0 rows affected
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc user1;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| name  | varchar(20)  | NO   | PRI |         |       |
| email | varchar(100) | YES  | UNI | NULL    |       |
| phone | varchar(11)  | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set

查看表创建语句：唯一约束已添加

mysql> show create table user1;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| user1 | CREATE TABLE `user1` (
  `name` varchar(20) NOT NULL,
  `email` varchar(100) default NULL,
  `phone` varchar(11) default NULL,
  PRIMARY KEY  (`name`),
  UNIQUE KEY `emailUnique` (`email`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

mysql> show index from user1;
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name    | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| user1 |          0 | PRIMARY     |            1 | name        | A         |           0 | NULL     | NULL   |      | BTREE      |         |
| user1 |          0 | emailUnique |            1 | email       | A         |           0 | NULL     | NULL   | YES  | BTREE      |         |
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
2 rows in set

删除唯一约束：注意删除约束的方式，是drop INDEX，而不是drop INDEX；

mysql> alter table user1 drop INDEX emailUnique;
Query OK, 0 rows affected
Records: 0  Duplicates: 0  Warnings: 0
mysql> show index from user1;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| user1 |          0 | PRIMARY  |            1 | name        | A         |           0 | NULL     | NULL   |      | BTREE      |         |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
1 row in set

mysql> show create table user1;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                           |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| user1 | CREATE TABLE `user1` (
  `name` varchar(20) NOT NULL,
  `email` varchar(100) default NULL,
  `phone` varchar(11) default NULL,
  PRIMARY KEY  (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

mysql> desc user1;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| name  | varchar(20)  | NO   | PRI |         |       |
| email | varchar(100) | YES  |     | NULL    |       |
| phone | varchar(11)  | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set
mysql> 

添加联合唯一约束：

mysql> alter table user1 add constraint email_Phone_Unique UNIQUE(email,phone);
Query OK, 0 rows affected
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc user1;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| name  | varchar(20)  | NO   | PRI |         |       |
| email | varchar(100) | YES  | MUL | NULL    |       |
| phone | varchar(11)  | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set

mysql> show create table user1;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                               |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| user1 | CREATE TABLE `user1` (
  `name` varchar(20) NOT NULL,
  `email` varchar(100) default NULL,
  `phone` varchar(11) default NULL,
  PRIMARY KEY  (`name`),
  UNIQUE KEY `email_Phone_Unique` (`email`,`phone`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

mysql> show index from user1;
+-------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name           | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| user1 |          0 | PRIMARY            |            1 | name        | A         |           0 | NULL     | NULL   |      | BTREE      |         |
| user1 |          0 | email_Phone_Unique |            1 | email       | A         |           0 | NULL     | NULL   | YES  | BTREE      |         |
| user1 |          0 | email_Phone_Unique |            2 | phone       | A         |           0 | NULL     | NULL   | YES  | BTREE      |         |
+-------+------------+--------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
3 rows in set

mysql>