Mysql Connot add foreign key constraint. how can I resolve it? - mysql

Question

I tried to excute the query. but a error was occurred. the error message is 'Cannot add foreign key constraint'.
I supposed to create this table. but it didn't work.
CREATE TABLE IF NOT EXISTS `mydb`.`member` (
`idseq` INT(1) NOT NULL AUTO_INCREMENT,
`id` VARCHAR(50) NOT NULL,
`pw` VARCHAR(20) NOT NULL,
`name` VARCHAR(50) NOT NULL,
`email` VARCHAR(45) NOT NULL,
`mobile0` VARCHAR(3) NOT NULL,
`mobile1` VARCHAR(3) NOT NULL,
`mobile2` VARCHAR(4) NOT NULL,
`mobile3` VARCHAR(4) NOT NULL,
`birth` DATE NOT NULL,
`admin_YN` VARCHAR(45) NOT NULL DEFAULT 'N',
`reg_date` DATE NOT NULL,
`upd_date` DATE NOT NULL,
PRIMARY KEY (`idseq`, `id`))
ENGINE = InnoDB
AUTO_INCREMENT = 6
DEFAULT CHARACTER SET = utf8;
CREATE TABLE IF NOT EXISTS `mydb`.`reservation` (
`reservation_seq` INT(11) NOT NULL AUTO_INCREMENT,
`user_id` VARCHAR(50) NOT NULL,
`playMv_seq` INT(11) NOT NULL,
`reservaion_seat_code` VARCHAR(20) NOT NULL,
`reservaion_seat_num` INT(11) NOT NULL,
`reservation_charge` VARCHAR(20) NOT NULL,
`reservation_date` DATETIME NOT NULL,
PRIMARY KEY (`reservation_seq`, `user_id`, `playMv_seq`),
FOREIGN KEY (`user_id`)
REFERENCES `mydb`.`member` (`id`)
)
ENGINE = InnoDB
AUTO_INCREMENT = 8
DEFAULT CHARACTER SET = utf8;
So I checked it detail from a query'show engine innodb status. the detail error message is
Error in foreign key constraint of table mydb/reservation:
FOREIGN KEY (`user_id`)
REFERENCES `mydb`.`member` (`id`)
Cannot find an index in the referenced table where the
referenced columns appear as the first columns, or column types
in the table and the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in
tables created with >= InnoDB-4.1.12, and such columns in old tables
cannot be referenced by such columns in new tables.
how can I resolve the error

Answer 1

You're trying to create a foreign key referencing the id column of the target table:
FOREIGN KEY (`user_id`)
REFERENCES `mydb`.`member` (`id`)
But what is the actual key on that target table?:
PRIMARY KEY (`idseq`, `id`)
It's not id, if the composite of idseq and id. In order to reference that as a foreign key, you need local columns which match that:
`user_idseq` INT(1) NOT NULL,
`user_id` VARCHAR(50) NOT NULL,
And use both of them for the foreign key:
FOREIGN KEY (`user_idseq`, `user_id`)
REFERENCES `mydb`.`member` (`idseq`, `id`)
(Side Note: That primary key in member looks pretty strange to me in the first place. Why can't idseq by itself be the primary key? What is the purpose of id?)