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我有两张桌子,一张是地板。每个楼层都可以包含房间,这些房间包含位于 Floor 表中的 Floor_ID 的外键。我一直在阅读关于 ON CASCADE DELETE 的文章,这似乎是我的答案,但我对我所读到的内容感到困惑。我知道我可以调用一个包含两个命令的例程,

DELETE FROM Room WHERE Floor_ID = floorID;
DELETE FROM Floor WHERE Floor_ID = floorID;

但是我怎么能使用 ON CASCADE DELETE 来执行同样的事情呢?删除楼层时,与该楼层关联的所有房间也将被删除。

CREATE TABLE `Floor` (
`Floor_ID` int(11) NOT NULL AUTO_INCREMENT,
`Hub_ID` int(11) NOT NULL,
`FloorNum` int(11) NOT NULL,
`FloorName` varchar(45) DEFAULT NULL,
`Timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`Hub_ID`,`FloorNum`),
UNIQUE KEY `Floor_ID_UNIQUE` (`Floor_ID`),
KEY `fk_Floor_Hub1_idx` (`Hub_ID`),
CONSTRAINT `fk_Floor_Hub1` FOREIGN KEY (`Hub_ID`) REFERENCES `Hub` (`Hub_ID`) ON DELETE   NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=124 DEFAULT CHARSET=latin1

CREATE TABLE `Room` (
`Room_ID` int(11) NOT NULL AUTO_INCREMENT,
`RoomLabel` varchar(45) NOT NULL,
`Floor_ID` int(11) NOT NULL,
`FloorArea` decimal(10,2) NOT NULL COMMENT 'Square feet',
`RoomHeight` decimal(10,2) DEFAULT NULL COMMENT 'Feet',
`Timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`Room_ID`),
KEY `fk_Room_Floor1_idx` (`Floor_ID`),
CONSTRAINT `fk_Room_Floor1` FOREIGN KEY (`Floor_ID`) REFERENCES `Floor` (`Floor_ID`) ON   DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=259 DEFAULT CHARSET=latin1
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您必须将外键约束定义为 ON DELETE CASCADE。目前,您将它们设置为 NO ACTION。当它们在 CASCADE 上时,所有引用已删除记录的记录也将被删除。

于 2013-05-27T16:24:56.087 回答