有趣的问题。您可能需要在调用
CREATE TABLE语句之前禁用外键，然后再启用它们。这将允许您直接在
CREATE TABLEDDL中定义外键：
例：
SET FOREIGN_KEY_CHECKS = 0;Query OK, 0 rows affected (0.00 sec)CREATE TABLE IF NOT EXISTS `rabbits` ( `id` INT UNSIGNED NOT NULL AUTO_INCREMENT, `name` VARCHAr(255) NOT NULL, `main_page_id` INT UNSIGNED COMMENT 'What page is the main one', PRIMARY KEY (`id`), KEY `main_page_id` (`main_page_id`), ConSTRAINT `fk_rabbits_main_page` FOREIGN KEY (`main_page_id`) REFERENCES `rabbit_pages` (`id`)) ENGINE=InnoDB;Query OK, 0 rows affected (0.04 sec)CREATE TABLE IF NOT EXISTS `rabbit_pages` ( `id` INT UNSIGNED NOT NULL AUTO_INCREMENT, `rabbit_id` INT UNSIGNED NOT NULL, `title` VARCHAr(255) NOT NULL, `content` TEXT NOT NULL, PRIMARY KEY (`id`), KEY `rabbit_id` (`rabbit_id`), ConSTRAINT `fk_rabbits_pages` FOREIGN KEY (`rabbit_id`) REFERENCES `rabbits` (`id`)) ENGINE=InnoDB;Query OK, 0 rows affected (0.16 sec)SET FOREIGN_KEY_CHECKS = 1;Query OK, 0 rows affected (0.00 sec)
测试用例：
INSERT INTO rabbits (name, main_page_id) VALUES ('bobby', NULL);Query OK, 1 row affected (0.02 sec)INSERT INTO rabbit_pages (rabbit_id, title, content) VALUES (1, 'My Main Page', 'Hello');Query OK, 1 row affected (0.00 sec)SELECt * FROM rabbits;+----+-------+--------------+| id | name | main_page_id |+----+-------+--------------+| 1 | bobby | NULL |+----+-------+--------------+1 row in set (0.00 sec)SELECt * FROM rabbit_pages;+----+-----------+--------------+---------+| id | rabbit_id | title | content |+----+-----------+--------------+---------+| 1 | 1 | My Main Page | Hello |+----+-----------+--------------+---------+1 row in set (0.00 sec)UPDATE rabbits SET main_page_id = 2 WHERe id = 1;ERROR 1452 (23000): A foreign key constraint failsUPDATE rabbits SET main_page_id = 1 WHERe id = 1;Query OK, 1 row affected (0.00 sec)Rows matched: 1 Changed: 1 Warnings: 0UPDATE rabbit_pages SET rabbit_id = 2 WHERe id = 1;ERROR 1452 (23000): A foreign key constraint fails
