MYSQL ERROR: Error 1215: Cannot add foreign key constraint

Question

I'm trying to forward engineer my ERD into scheme in workbench 6.0 but I'm getting this error. I've checked all column types and they're the same. I looked through similar questions here but still cannot find an answer. Here's the error log:

xecuting SQL script in server

ERROR: Error 1215: Cannot add foreign key constraint







-- -----------------------------------------------------

-- Table `proj`.`employee`

-- -----------------------------------------------------

CREATE TABLE IF NOT EXISTS `proj`.`employee` (

  `employee_id` INT NOT NULL,

  `position_id` INT NOT NULL,

  PRIMARY KEY (`employee_id`),

  CONSTRAINT `fk_employee_employee_history1`

    FOREIGN KEY (`employee_id`)

    REFERENCES `proj`.`employee_history` (`employee_id`)

    ON DELETE NO ACTION

    ON UPDATE NO ACTION,

  CONSTRAINT `fk_employee_equipment_rentals1`

    FOREIGN KEY (`employee_id`)

    REFERENCES `proj`.`equipment_rentals` (`handling_employee_id`)

    ON DELETE NO ACTION

    ON UPDATE NO ACTION,

  CONSTRAINT `fk_employee_scheduled_trips1`

    FOREIGN KEY (`employee_id`)

    REFERENCES `proj`.`scheduled_trips` (`leader`)

    ON DELETE NO ACTION

    ON UPDATE NO ACTION,

  CONSTRAINT `fk_employee_scheduled_trips2`

    FOREIGN KEY (`employee_id`)

    REFERENCES `proj`.`scheduled_trips` (`assistant`)

    ON DELETE NO ACTION

    ON UPDATE NO ACTION)

ENGINE = InnoDB



SQL script execution finished: statements: 8 succeeded, 1 failed



Fetching back view definitions in final form.

Nothing to fetch

Answer 1

So it turns out my foreign key constraints were all messed up. I had the relationships backwards. Instead of having the foreign keys reference the primary keys, I was having the primary keys BE the foreign keys referencing the non unique columns. I reversed that, and it worked.