mysql的外鍵怎么寫

mysql的外鍵怎么寫

mysql的外鍵怎么寫?

mysql添加外鍵:

為已經添加好的數據表添加外鍵:

語法:

alter?table?表名?add?constraint?FK_ID?foreign?key(你的外鍵字段名)?REFERENCES?外表表名(對應的表的主鍵字段名);

例:?

alter?table?tb_active?add?constraint?FK_ID?foreign?key(user_id)?REFERENCES?tb_user(id) //FK_ID是外鍵的名稱 /* CREATE?TABLE?`tb_active`?( `id`?int(11)?NOT?NULL?AUTO_INCREMENT, `title`?varchar(100)?CHARACTER?SET?utf8?COLLATE?utf8_unicode_ci?NOT?NULL, `content`?text?CHARACTER?SET?utf8?COLLATE?utf8_unicode_ci?NOT?NULL, `user_id`?int(11)?NOT?NULL, PRIMARY?KEY?(`id`), KEY?`user_id`?(`user_id`), KEY?`user_id_2`?(`user_id`), CONSTRAINT?`FK_ID`?FOREIGN?KEY?(`user_id`)?REFERENCES?`tb_user`?(`id`) )?ENGINE=InnoDB?default?CHARSET=latin1 */

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