Question

我试图这样做：

ALTER TABLE `chiang`.`Standings`  
  ADD CONSTRAINT `Team` FOREIGN KEY (`Team`) REFERENCES `chiang`.`Teams`(`ID`) ON UPDATE CASCADE ON DELETE RESTRICT;

但是我收到了这个错误：

Can't write; duplicate key in table '#sql-6f42_12d414'

我有一些引用team.ID的外键。这是什么导致它？我怎么能绕过它？

DB Schema：

/*Table structure for table `Games` */

DROP TABLE IF EXISTS `Games`;

CREATE TABLE `Games` (
  `HomeID` int(11) NOT NULL,
  `AwayID` int(11) NOT NULL,
  `HomeScore` int(11) NOT NULL,
  `AwayScore` int(11) NOT NULL,
  `Date` date NOT NULL,
  `ResultID` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`ResultID`),
  UNIQUE KEY `ResultID_UNIQUE` (`ResultID`),
  KEY `HomeTeeam_idx` (`HomeID`),
  KEY `AwayTeam_idx` (`AwayID`),
  CONSTRAINT `AwayTeam` FOREIGN KEY (`AwayID`) REFERENCES `Teams` (`ID`) ON UPDATE CASCADE,
  CONSTRAINT `HomeTeam` FOREIGN KEY (`HomeID`) REFERENCES `Teams` (`ID`) ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

/*Data for the table `Games` */

/*Table structure for table `PlayerResults` */

DROP TABLE IF EXISTS `PlayerResults`;

CREATE TABLE `PlayerResults` (
  `PlayerID` int(11) NOT NULL,
  `GameID` int(11) NOT NULL,
  `TeamID` int(11) NOT NULL,
  `POS` varchar(45) NOT NULL,
  `MP` time NOT NULL,
  `FG` int(11) NOT NULL,
  `FGA` int(11) NOT NULL,
  `3P` int(11) NOT NULL,
  `3PA` int(11) NOT NULL,
  `FT` int(11) NOT NULL,
  `FTA` int(11) NOT NULL,
  `ORB` int(11) NOT NULL,
  `DRB` int(11) NOT NULL,
  `TRB` int(11) NOT NULL,
  `AST` int(11) NOT NULL,
  `STL` int(11) NOT NULL,
  `BLK` int(11) NOT NULL,
  `TOV` int(11) NOT NULL,
  `PF` int(11) NOT NULL,
  `PTS` int(11) NOT NULL,
  `PlusMinus` int(11) NOT NULL,
  PRIMARY KEY (`PlayerID`,`GameID`),
  CONSTRAINT `Player` FOREIGN KEY (`PlayerID`) REFERENCES `Players` (`ID`) ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

/*Data for the table `PlayerResults` */

/*Table structure for table `Players` */

DROP TABLE IF EXISTS `Players`;

CREATE TABLE `Players` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `FirstName` varchar(45) NOT NULL,
  `LastName` varchar(45) NOT NULL,
  `Team` int(11) NOT NULL,
  PRIMARY KEY (`ID`,`FirstName`,`LastName`,`Team`),
  KEY `Team_idx` (`Team`),
  CONSTRAINT `Team` FOREIGN KEY (`Team`) REFERENCES `Teams` (`ID`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

/*Data for the table `Players` */

/*Table structure for table `Standings` */

DROP TABLE IF EXISTS `Standings`;

CREATE TABLE `Standings` (
  `Team` int(11) NOT NULL,
  `Wins` int(11) NOT NULL DEFAULT '0',
  `Losses` int(11) NOT NULL DEFAULT '0',
  `Year` year(4) NOT NULL,
  PRIMARY KEY (`Team`,`Year`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

/*Data for the table `Standings` */

/*Table structure for table `Teams` */

DROP TABLE IF EXISTS `Teams`;

CREATE TABLE `Teams` (
  `ID` int(11) NOT NULL,
  `Name` varchar(45) NOT NULL,
  `City` varchar(45) NOT NULL,
  `Acronym` varchar(45) NOT NULL,
  PRIMARY KEY (`ID`),
  UNIQUE KEY `ID_UNIQUE` (`ID`),
  UNIQUE KEY `Name_UNIQUE` (`Name`),
  UNIQUE KEY `City_UNIQUE` (`City`),
  UNIQUE KEY `Acronym_UNIQUE` (`Acronym`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

/*Data for the table `Teams` */

Answer 1

根据Foreign key constraints

的文件

如果给出了CONSTRAINT符号子句，则符号值在数据库中必须是唯一的。如果没有给出该子句，InnoDB会自动创建名称。

请注意，从版本5.0.38开始，InnoDB允许列上有两个或更多外键，它们可能引用不同的表/列。它甚至允许具有相同定义但具有不同约束名称的外键。

Constraint名称必须是跨数据库的唯一。

ALTER TABLE `chiang`.`Standings`  
  ADD CONSTRAINT `Team` 
      FOREIGN KEY (`Team`) 
      REFERENCES `chiang`.`Teams`(`ID`) 
        ON UPDATE CASCADE 
        ON DELETE RESTRICT;

失败。因为，您已经在表Team中定义了名为Players的约束。

CREATE TABLE `Players` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `FirstName` varchar(45) NOT NULL,
  `LastName` varchar(45) NOT NULL,
  `Team` int(11) NOT NULL,
  PRIMARY KEY (`ID`,`FirstName`,`LastName`,`Team`),
  KEY `Team_idx` (`Team`),

  CONSTRAINT `Team` 
    FOREIGN KEY (`Team`) 
    REFERENCES `Teams` (`ID`) 
      ON DELETE CASCADE 
      ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

确保为在数据库中的任何表上定义的每个约束定义UNIQUE。

Answer 2

SET FOREIGN_KEY_CHECKS = 0;

[your query here]

SET FOREIGN_KEY_CHECKS = 1;

多个外键引用一列给出错误

2 个答案: