删除唯一性约束
语法如下：
alter table tableName drop index key_name;#删除唯一性约束，实际就是删除索引
drop index key_name on tableName; #两种方法均可
mysql> show create table t_user;+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| Table | Create Table |+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| t_user | CREATE TABLE `t_user` (`id` int(10) DEFAULT NULL,`name` varchar(32) NOT NULL,`email` varchar(128) DEFAULT NULL,UNIQUE KEY `name` (`name`,`email`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)
mysql> alter table t_user drop index name;
mysql> show create table t_user;+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| Table | Create Table|+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| t_user | CREATE TABLE `t_user` (`id` int(10) DEFAULT NULL,`name` varchar(32) NOT NULL,`email` varchar(128) DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)
