Question

I know this question is posted a lot, and I’ve checked my code carefully but couldn’t find the reason why when I create the table with Foreign Key, mysql gives me an error.

mysql> CREATE TABLE Act_Model(
    -> code VARCHAR(8) NOT NULL,
    -> model VARCHAR(64) NOT NULL,
    -> PRIMARY KEY (code))ENGINE = INNODB;
Query OK, 0 rows affected (0.09 sec)
mysql> CREATE TABLE IBT_ActItem(
    -> model VARCHAR(64) NOT NULL,
    -> flagbit BIGINT(20) UNSIGNED NOT NULL DEFAULT '0',
    -> PRIMARY KEY(model),
    -> FOREIGN KEY( model) REFERENCES Act_Model(model))ENGINE = INNODB;
ERROR 1005 (HY000): Can't create table 'test.ibt_actitem' (errno: 150)
mysql> CREATE TABLE IBT_ActItem(
    -> model VARCHAR(64) NOT NULL,
    -> flagbit BIGINT(20) UNSIGNED NOT NULL DEFAULT '0',
    -> PRIMARY KEY(model))ENGINE = INNODB;
Query OK, 0 rows affected (0.09 sec)

when I used show engins;, for InnoDB it gave me:

| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |

Can you help me to find where is my mistake? Thanks

Answer 1

You need to add a unique index on the model column in the parent table:

CREATE TABLE Act_Model(
 code VARCHAR(8) NOT NULL,
 model VARCHAR(64) NOT NULL,
 PRIMARY KEY (code),
 UNIQUE KEY model (model)
 )ENGINE = INNODB;