- 建表時創建外鍵:
CREATE TABLE`xh` (
`id` int(100) unsigned NOT NULL AUTO_INCREMENT COMMENT ,
`cl_id` smallint(3) unsigned NOT NULL COMMENT,
`title` varchar(100) COLLATE utf8_unicode_ci NOT NULL COMMENT ,
`details` text COLLATE utf8_unicode_ci NOT NULL COMMENT ,
`date` datetime NOT NULL COMMENT ,
`au_id` smallint(6) unsigned NOT NULL COMMENT ,
`click` int(100) unsigned NOT NULL DEFAULT '0' COMMENT ,
`reco` int(100) unsigned NOT NULL DEFAULT '0' COMMENT,
PRIMARY KEY (`id`),
KEY `fk_class` (`cl_id`),
CONSTRAINT `fk_class`FOREIGN KEY (`cl_id`) REFERENCES `fl` (`id`),
KEY `fk_author` (`au_id`),
CONSTRAINT `fk_author` FOREIGN KEY (`au_id`) REFERENCES `author` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
- 建表後創建外鍵:
Alter Table `ym` Add Constraint `fk_author` Foreign Key (`au_id`) References `author` (`id`);
- 查看錶結構:
Show Create Table `ym`;
4.級聯: 在末尾可加上(可單獨添加,也可全部添加):
ON UPDATE CASCADE(級聯更新)
ON DELETE CASCADE(級聯刪除)
比如:
ALTER TABLE `ym` ADD CONSTRAINT `fk_author` FOREIGN KEY (`au_id`)