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我查看了 MySQL 5.1 文档，但仍然无法弄清楚——因为我注意到我输入到 MySQL 的代码和系统输出的代码之间存在差异。

代码示例 01 和 02 之间有什么区别，这意味着 02CONSTRAINT之前添加了FOREIGN KEY- 为什么，它是做什么的？

CODE_SAMPLE_01：

FOREIGN KEY (TABLE_02_nID_FK__TABLE_01_sID_PK) REFERENCES TABLE_01(TABLE_01_sID_PK),

语境：

CREATE TABLE `TABLE_02` (
  `TABLE_02_sID_PK` int(8) NOT NULL,
  `TABLE_02_nID_FK__TABLE_01_sID_PK` int(8) NOT NULL,
  `TABLE_02_cID` int(8) NOT NULL,
  `TABLE_02_data01` varchar(128) default NULL,
  `TABLE_02_data02` varchar(128) NOT NULL,
  `create_timestamp` DATETIME DEFAULT NULL,
  `update_timestamp` TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`TABLE_02_sID_PK`),
  FOREIGN KEY (TABLE_02_nID_FK__TABLE_01_sID_PK) REFERENCES TABLE_01(TABLE_01_sID_PK),
  INDEX `TABLE_02_nID_FK__TABLE_01_sID_PK` (`TABLE_02_nID_FK__TABLE_01_sID_PK`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CODE_SAMPLE_02：

CONSTRAINT `table_02_ibfk_1` FOREIGN KEY (`TABLE_02_nID_FK__TABLE_01_sID_PK`) REFERENCES `table_01` (`TABLE_01_sID_PK`)

语境：

CREATE TABLE `table_02` (
  `TABLE_02_sID_PK` int(8) NOT NULL,
  `TABLE_02_nID_FK__TABLE_01_sID_PK` int(8) NOT NULL,
  `TABLE_02_cID` int(8) NOT NULL,
  `TABLE_02_data01` varchar(128) DEFAULT NULL,
  `TABLE_02_data02` varchar(128) NOT NULL,
  `create_timestamp` datetime DEFAULT NULL,
  `update_timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`TABLE_02_sID_PK`),
  KEY `TABLE_02_nID_FK__TABLE_01_sID_PK` (`TABLE_02_nID_FK__TABLE_01_sID_PK`),
  CONSTRAINT `table_02_ibfk_1` FOREIGN KEY (`TABLE_02_nID_FK__TABLE_01_sID_PK`) REFERENCES `table_01` (`TABLE_01_sID_PK`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
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1 回答 1

11

可选的 CONSTRAINT 关键字允许您指定外键的名称。没有它，将自动生成一个名称。

此名称可以在INFORMATION_SCHEMA TABLE_CONSTRAINTS表中看到。

于 2010-12-03T21:14:58.153 回答