Question

我有两张桌子，一张是Floor。每个楼层可以包含房间，其中包含位于楼层表中的Floor_ID的外键。我一直在阅读关于ON CASCADE DELETE的内容，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;

但是我如何使用ON CASCADE DELETE来执行相同的操作呢？删除楼层时，与该楼层相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

Answer 1

您必须将外键约束定义为ON DELETE CASCADE。目前，您将它们视为无操作。当他们使用CASCADE时，所有引用已删除记录的记录也将被删除。

删除父记录时如何删除所有子记录？

1 个答案: