mysql errno: 150 “Foreign key constraint is incorrectly formed”- MariaDB

问题

MESSAGE_MAP TABLE

    CREATE TABLE `message_map` (
      `message_from` varchar(15) NOT NULL,
      `message_id` varchar(15) NOT NULL,
      `message_to` varchar(15) NOT NULL,
      `message_status` bit(1) DEFAULT NULL
    ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
  ALTER TABLE `message_map`
  ADD PRIMARY KEY (`message_from`,`message_id`,`message_to`),
  ADD KEY `FK_ij6tystusydqijqp8lgoigo1c` (`message_id`),

USER TABLE

 CREATE TABLE `user` (
      `USER_ID` varchar(15) NOT NULL,
      `PASSWORD` varchar(15) DEFAULT NULL,
      `PHONE_NUMBER` varchar(15) DEFAULT NULL,
      `USER_NAME` varchar(15) DEFAULT NULL,
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
   ALTER TABLE `user`
  ADD PRIMARY KEY (`USER_ID`),
  ADD UNIQUE KEY `USER_ID_UNIQUE` (`USER_ID`);

I tried below query to apply Foreign Key Constraint

ALTER TABLE `demo`.`message_map` 
ADD CONSTRAINT `FK_MSG_MAP_USER`
  FOREIGN KEY (`message_from`)
  REFERENCES `demo`.`user` (`USER_ID`)
  ON DELETE CASCADE
  ON UPDATE CASCADE,
ADD CONSTRAINT `FK_MSG_MAP_USER_TO`
  FOREIGN KEY (`message_to`)
  REFERENCES `demo`.`user` (`USER_ID`)
  ON DELETE CASCADE
  ON UPDATE CASCADE;

Im getting the following error

ERROR 1005: Can't create table <shema>.#sql-1964_4 (errno: 150 >"Foreign key constraint is incorrectly formed")

My Observation

The data type of the columns (message_from,message_to) and USER_ID are the same. And also USER_ID is a primary key.

Question is

What went wrong?

Thank you for the answers

回答1:

First there are a number of errors in your code that makes it a bit cumbersome to test. Second, make sure you use the same charset in both tables, I changed message_map to utf8:

DROP TABLE message_map;
CREATE TABLE message_map (
  message_from varchar(15) NOT NULL,
  message_id varchar(15) NOT NULL,
  message_to varchar(15) NOT NULL,
  message_status bit(1) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

ALTER TABLE message_map
    ADD PRIMARY KEY (message_from,message_id,message_to),
    ADD KEY FK_ij6tystusydqijqp8lgoigo1c (message_id);

ALTER TABLE message_map 
    ADD CONSTRAINT FK_MSG_MAP_USER
    FOREIGN KEY (message_from)
        REFERENCES user (USER_ID)
            ON DELETE CASCADE
            ON UPDATE CASCADE,
    ADD CONSTRAINT FK_MSG_MAP_USER_TO
    FOREIGN KEY (message_to)
        REFERENCES user (USER_ID)
            ON DELETE CASCADE
            ON UPDATE CASCADE;

I removed demo from the foreign key definition.

来源：https://stackoverflow.com/questions/41361838/mysql-errno-150-foreign-key-constraint-is-incorrectly-formed-mariadb

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mysql

mariadb

foreign-key-relationship

mysql-error-1005