MySQL FK 错误 1005 - 与 FK 相同的 PK

Question

我有一个类似的问题: How to create foreign key that is also a primary key in MySQL?

但是我的架构似乎与答案匹配，但仍然返回错误“ERROR 1005 (HY000): Can't create table (errno:150)”

CREATE TABLE po_items (
job_id          CHAR(3) NOT NULL,
po_id           CHAR(3) NOT NULL,
item_id     CHAR(3) NOT NULL,
quantity        SMALLINT,
PRIMARY KEY (job_id, po_id, item_id),
FOREIGN KEY (job_id, po_id) REFERENCES pos(job_id, po_id)
) ENGINE = INNODB;

CREATE TABLE items (
item_id         CHAR(3) NOT NULL,
descr       CHAR(10),
on_hand         SMALLINT,
price           DECIMAL(5,2),
PRIMARY KEY (item_id),
FOREIGN KEY (item_id) REFERENCES po_items(item_id)
) ENGINE = INNODB;

提前致谢

Answer 1

要定义外键，引用的字段必须已建立索引。

根据有关外键约束的文档:

REFERENCES tbl_name (index_col_name,...)

在表 po_items 中的 item_id 上定义一个 INDEX，它应该可以工作。

CREATE TABLE po_items (
job_id          CHAR(3) NOT NULL,
po_id           CHAR(3) NOT NULL,
item_id     CHAR(3) NOT NULL,
quantity        SMALLINT,
KEY (item_id),
PRIMARY KEY (job_id, po_id, item_id),
FOREIGN KEY (job_id, po_id) REFERENCES pos(job_id, po_id)
) ENGINE = INNODB;

引用:

• MySQL Using FOREIGN KEY Constraints

[CONSTRAINT [symbol]] FOREIGN KEY
[index_name] (index_col_name, ...)
REFERENCES tbl_name (index_col_name,...)
[ON DELETE reference_option]
[ON UPDATE reference_option]

reference_option:
RESTRICT | CASCADE | SET NULL | NO ACTION