mysql在表中添加多个外键/增加外键/级联约束_MySQL
程序员文章站
2022-05-08 21:42:48
...
Mysql外键
bitsCN.com
bitsCN.com
mysql在表中添加多个外键/增加外键/级联约束
1. 建表时创建外键: 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 2. 建表后创建外键: Alter Table `ym` Add Constraint `fk_author` Foreign Key (`au_id`) References `author` (`id`); 3. 查看表结构: Show Create Table `ym`; 4.级联: 在末尾可加上(可单独添加,也可全部添加):ON UPDATE CASCADE(级联更新)ON DELETE CASCADE(级联删除) 比如:ALTER TABLE `ym` ADD CONSTRAINT `fk_author` FOREIGN KEY (`au_id`) REFERENCES `author` (`id`) ON UPDATE CASCADE
bitsCN.com
下一篇: 讲解php如何从字符串中创建函数