MySQL：错误1822（HY000）无法添加外键约束。缺少约束的索引

Question

我正在尝试使用外键创建表。当我按如下所示执行CREATE TABLE语句时，收到此错误消息。

ERROR 1822 (HY000): Failed to add the foreign key constraint. Missing index for constraint 'fk_opentran_helper' in the referenced table 'helper'

CREATE TABLE语句

CREATE TABLE helper_work_day(
work_day_id TINYINT,
helper_id SMALLINT(4) NOT NULL,
office_code DECIMAL(10) NOT NULL,
work_day TINYINT NOT NULL,
kana VARCHAR(32) NOT NULL,
can_holiday_work BIT(1) NOT NULL,
CONSTRAINT pk_open_transaction PRIMARY KEY (office_code, helper_id, work_day_id),
CONSTRAINT fk_opentran_helper FOREIGN KEY (helper_id) references helper (id),
CONSTRAINT fk_opentran_office FOREIGN KEY (office_code) references office (office_code)
);

'helper'TABLE的信息

mysql> SHOW COLUMNS FROM helper;
+------------------+---------------+------+-----+---------+-------+
| Field            | Type          | Null | Key | Default | Extra |
+------------------+---------------+------+-----+---------+-------+
| id               | smallint(4)   | NO   | PRI | NULL    |       |
| office_code      | decimal(10,0) | NO   | PRI | NULL    |       |
| name             | varchar(32)   | NO   |     | NULL    |       |
| kana             | varchar(32)   | NO   |     | NULL    |       |
| can_holiday_work | bit(1)        | NO   |     | NULL    |       |
| login_id         | varchar(16)   | NO   |     | NULL    |       |
| password         | char(60)      | NO   |     | NULL    |       |
+------------------+---------------+------+-----+---------+-------+
7 rows in set (0.04 sec)

mysql> SHOW INDEX FROM helper;
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table  | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| helper |          0 | PRIMARY  |            1 | office_code | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
| helper |          0 | PRIMARY  |            2 | id          | A         |           0 |     NULL |   NULL |      | BTREE      |         |               | YES     | NULL       |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
2 rows in set (0.06 sec)

我尝试过的

• 确保'helper'表中的'id'列具有索引
• 确保'id'列（'helper'表）和'helper_id'列（'helper_work_day'表）具有相同的数据类型

Answer 1

由于Slava Rozhnev的评论，我成功创建了该表。我用此语句添加了id列的索引（在“ helper”表中）。

ALTER TABLE helper ADD INDEX index_id(id);