Question

Ok, so I am creating tables in MySQL with indexes and foreign keys. I use MySQL Workbench to create the tables and then have it forward engineer a SQL create script (I do better in a visual DB environment than just writing out the SQL code by hand right away).

The problem is many times when I import the sql script into mysql, I get the classic eror:

#1005 - Can't create table 'db.tablename' (errno: 121) 

I’ve managed to figure out the problem each time, usually index/foreign key related, but now I’m starting to get irritated at having to fix it each time. I don’t really understand what the problem is (especially when a MySQL product is creating sql code for its own database). Below is some code that typically causes the problem.

CREATE  TABLE IF NOT EXISTS `db`.`groupMembers` (
  `groupMembersID` INT NOT NULL AUTO_INCREMENT ,
  `groupID` INT NOT NULL ,
  `userID` INT NULL ,
  PRIMARY KEY (`groupMembersID`) ,
  INDEX `group` (`groupID` ASC) ,
  INDEX `user` (`userID` ASC) ,
  CONSTRAINT `group`
    FOREIGN KEY (`groupID` )
    REFERENCES `db`.`groups` (`groupsID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE,
  CONSTRAINT `user`
    FOREIGN KEY (`userID` )
    REFERENCES `db`.`users` (`usersID` )
    ON DELETE CASCADE
    ON UPDATE CASCADE)
ENGINE = InnoDB;

The error usually comes from the first INDEX definition – even when I take out the index definition, I just get the error at the the first foreign key constraint definition. I’ve checked, and the foreign key remote column and the local column are the same data-type and size.

Answer 1

“errno 121 means a duplicate key error”

Constraints must have an unique name in the database, you might wanna change your FK names. Like so, FK_groupMembers_group and FK_groupMembers_user.