错误代码：1215：无法添加外键约束

Question

因此，我在 MySQL 中创建了以下表格。

    CREATE TABLE `StockTransaction` (
    `TransactionID` int(11),
    `Fee` decimal(6,2),
    `DateTime` datetime DEFAULT NULL,
    `PricePerShare` decimal(6,2),
    PRIMARY KEY (`TransactionID`)
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

# Dump of table StockOrder
# ------------------------------------------------------------

DROP TABLE IF EXISTS `StockOrder`;

CREATE TABLE `StockOrder` (
  `OrderID` int(11) NOT NULL,
  `OrderStockSymbol` char(6) NOT NULL,
  `OrderType` enum('buy','sell') DEFAULT NULL,
  `NumOfShares` int(11) DEFAULT NULL,
  `OrderCustomerAccNum` int(11) unsigned NOT NULL,
  `DateOfOrder` datetime DEFAULT NULL,
  `PriceType` enum('Market','MarketOnClose','TrailingStop','HiddenStop') NOT NULL,
  `OrderEmployeeID` int(11) unsigned DEFAULT NULL,
  `OrderCustomerID` int(11) unsigned NOT NULL,
  `OrderTransactionID` int(11) unsigned,
  `Type` char(30) NOT NULL DEFAULT 'Default',
  PRIMARY KEY (`OrderID`,`Type`),
  CONSTRAINT `stockorder_ibfk_1` FOREIGN KEY (`OrderStockSymbol`) REFERENCES `Stock` (`StockSymbol`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_2` FOREIGN KEY (`OrderCustomerAccNum`) REFERENCES `Account` (`AccountNumber`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_3` FOREIGN KEY (`OrderCustomerID`) REFERENCES `Customer` (`SSN`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_4` FOREIGN KEY (`OrderEmployeeID`) REFERENCES `Employee` (`EmployeeSSN`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_5` FOREIGN KEY (`OrderTransactionID`) REFERENCES `StockTransaction` (`TransactionID`) ON DELETE NO ACTION ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

无论出于何种原因，如果我注释掉约束 'stockorder_ibfk_5' 的创建，此代码有效，但对于我的生活我无法弄清楚为什么。到底发生了什么，为什么我不能创建 StockTransaction.TransactionID?

的外键

Answer 1

类型不匹配。 StockOrder.OrderTransactionID 是 无符号的 ，而 StockTransaction.TransactionID 是 有符号的 。让它们都签名或未签名，你应该闪闪发光。

Answer 2

您在哪个字段上创建外键和引用的字段架构应该完全相同，一个是签名的（默认），另一个是未签名的。所以你的架构应该如下 -

CREATE TABLE `StockTransaction` (
    `TransactionID` int(11) unsigned,
    `Fee` decimal(6,2),
    `DateTime` datetime DEFAULT NULL,
    `PricePerShare` decimal(6,2),
    PRIMARY KEY (`TransactionID`)
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

# Dump of table StockOrder
# ------------------------------------------------------------

DROP TABLE IF EXISTS `StockOrder`;

CREATE TABLE `StockOrder` (
  `OrderID` int(11) NOT NULL,
  `OrderStockSymbol` char(6) NOT NULL,
  `OrderType` enum('buy','sell') DEFAULT NULL,
  `NumOfShares` int(11) DEFAULT NULL,
  `OrderCustomerAccNum` int(11) unsigned NOT NULL,
  `DateOfOrder` datetime DEFAULT NULL,
  `PriceType` enum('Market','MarketOnClose','TrailingStop','HiddenStop') NOT NULL,
  `OrderEmployeeID` int(11) unsigned DEFAULT NULL,
  `OrderCustomerID` int(11) unsigned NOT NULL,
  `OrderTransactionID` int(11) unsigned,
  `Type` char(30) NOT NULL DEFAULT 'Default',
  PRIMARY KEY (`OrderID`,`Type`),
  CONSTRAINT `stockorder_ibfk_1` FOREIGN KEY (`OrderStockSymbol`) REFERENCES `Stock` (`StockSymbol`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_2` FOREIGN KEY (`OrderCustomerAccNum`) REFERENCES `Account` (`AccountNumber`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_3` FOREIGN KEY (`OrderCustomerID`) REFERENCES `Customer` (`SSN`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_4` FOREIGN KEY (`OrderEmployeeID`) REFERENCES `Employee` (`EmployeeSSN`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `stockorder_ibfk_5` FOREIGN KEY (`OrderTransactionID`) REFERENCES `StockTransaction` (`TransactionID`) ON DELETE NO ACTION ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

注意：此外，我认为您希望将两个表中的主键都保留为 auto_increment，但根据您的要求，这不是必需的。

错误代码：1215：无法添加外键约束

Error Code: 1215: Cannot add foreign key constraint

mysql

sql

constraints