简单的表格 - 错误1215：无法添加外键约束，

Question

我有这两个简单的表

CREATE TABLE `location_main_master` (
    `location_main_master_id` bigint(16) unsigned NOT NULL, 
    `city_id_test` int(10) unsigned NOT NULL, 
    PRIMARY KEY (`location_main_master_id`,`city_id_test`), 
    UNIQUE KEY `location_main_master_id_UNIQUE` (`location_main_master_id`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8; 


CREATE TABLE `location_sub_master` (
    `location_sub_master_id` bigint(16) unsigned NOT NULL, 
    `city_id` int(10) unsigned NOT NULL, 
    PRIMARY KEY (`location_sub_master_id`,`city_id`), 
    UNIQUE KEY `location_sub_master_id_UNIQUE` (`location_sub_master_id`), 
    KEY `fk_location_sub_master_city_id_idx` (`city_id`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8; 

我想添加一个外键

ALTER TABLE `location_sub_master` 
ADD CONSTRAINT `fk_location_sub_city_id` 
    FOREIGN KEY (`city_id`) 
    REFERENCES `location_main_master` (`city_id_test`) 
    ON DELETE NO ACTION 
    ON UPDATE NO ACTION; 

它给我这个错误：

错误1215：无法添加外键约束

Answer 1

您必须更改主表中主键的顺序。

PRIMARY KEY（city_id_test，location_main_master_id）

所以，你的主表应该像

CREATE TABLE location_main_master（
location_main_master_id BIGINT（16）UNSIGNED NOT NULL，
city_id_test INT（10）UNSIGNED NOT NULL，
PRIMARY KEY（city_id_test，location_main_master_id），
UNIQUE KEY location_main_master_id_UNIQUE（location_main_master_id）
）ENGINE = INNODB DEFAULT CHARSET = utf8;