如何从MySQL表中删除唯一性约束？
您可以为此使用DROPINDEX。语法如下-
alter table yourTablename drop index yourUniqueName;
为了理解上述语法，让我们创建一个表。创建表的查询如下-
mysql> create table removeUniquenessConstraint -> ( -> Id int, -> Name varchar(100), -> Age int, -> isGreaterThan18 bool, -> UNIQUE(Id,isGreaterThan18) -> );
现在，借助SHOWCREATE命令检查表的详细信息。查询如下-
mysql> show create table removeUniquenessConstraint;
这是输出-
+----------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +----------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | removeUniquenessConstraint | CREATE TABLE `removeuniquenessconstraint` (`Id` int(11) DEFAULT NULL,`Name` varchar(100) DEFAULT NULL,`Age` int(11) DEFAULT NULL,`isGreaterThan18` tinyint(1) DEFAULT NULL,UNIQUE KEY `Id` (`Id`,`isGreaterThan18`)) ENGINE =InnoDB DEFAULT CHARSET =utf8 | +----------------------------+--------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
以下是从MySQL表中删除唯一性约束的查询-
mysql> alter table removeUniquenessConstraint drop index `Id`; Records: 0 Duplicates: 0 Warnings: 0
让我们再次检查表的所有详细信息。查询如下-
mysql> show create table removeUniquenessConstraint;
这是输出-
+----------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +----------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | removeUniquenessConstraint | CREATE TABLE `removeuniquenessconstraint` (`Id` int(11) DEFAULT NULL,`Name` varchar(100) DEFAULT NULL,`Age` int(11) DEFAULT NULL,`isGreaterThan18` tinyint(1) DEFAULT NULL) ENGINE =InnoDB DEFAULT CHARSET =utf8 | +----------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
查看上面的示例输出，没有唯一性约束。