1. 单列唯一性约束
a. 直接建表
CREATE TABLE t1
(
id
INT NOT NULL ,
uname
VARCHAR( 20 ) NOT NULL ,
PRIMARY KEY ( id
) ,
UNIQUE (uname
)) ENGINE = MYISAM ;
b. 删除唯一性约束
ALTER TABLE t1
DROP INDEX uname
c. 添加唯一性约束
ALTER TABLE t1
ADD UNIQUE (uname
)
2. 2列联合唯一性约束
a. 直接建表
CREATE TABLE t1
(
id
int(11) NOT NULL AUTO_INCREMENT,
user
int(11) NOT NULL,
subacount
varchar(40) NOT NULL,
PRIMARY KEY (id
),
UNIQUE KEY user
(user
,subacount
)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
b. 删除联合唯一性约束
ALTER TABLE t1
DROP INDEX user
c. 添加联合唯一性约束
ALTER TABLE t1
ADD UNIQUE user
(user
,subacount
)