删除 索引 外键 mysql_MySQL无法删除外键约束所需的索引(MySQL Cannot drop index needed in a foreign key constraint)...

MySQL无法删除外键约束所需的索引(MySQL Cannot drop index needed in a foreign key constraint)

我需要ALTER我现有的数据库来添加一列。 因此，我还要更新UNIQUE字段以包含该新列。 我试图删除当前的索引，但是不断得到错误MySQL Cannot drop index needed in a foreign key constraint

CREATE TABLE mytable_a (

ID TINYINT NOT NULL AUTO_INCREMENT PRIMARY KEY,

Name VARCHAR(255) NOT NULL,

UNIQUE(Name)

) ENGINE=InnoDB;

CREATE TABLE mytable_b (

ID TINYINT NOT NULL AUTO_INCREMENT PRIMARY KEY,

Name VARCHAR(255) NOT NULL,

UNIQUE(Name)

) ENGINE=InnoDB;

CREATE TABLE mytable_c (

ID TINYINT NOT NULL AUTO_INCREMENT PRIMARY KEY,

Name VARCHAR(255) NOT NULL,

UNIQUE(Name)

) ENGINE=InnoDB;

CREATE TABLE `mytable` (

`ID` int(11) NOT NULL AUTO_INCREMENT,

`AID` tinyint(5) NOT NULL,

`BID` tinyint(5) NOT NULL,

`CID` tinyint(5) NOT NULL,

PRIMARY KEY (`ID`),

UNIQUE KEY `AID` (`AID`,`BID`,`CID`),

KEY `BID` (`BID`),

KEY `CID` (`CID`),

CONSTRAINT `mytable_ibfk_1` FOREIGN KEY (`AID`) REFERENCES `mytable_a` (`ID`) ON DELETE CASCADE,

CONSTRAINT `mytable_ibfk_2` FOREIGN KEY (`BID&#