Cannot add or update a child row: a foreign key constraint fails (`company`.`employee`, CONSTRAINT.

 Cannot add or update a child row: a foreign key constraint fails (`company`.`employee`, CONSTRAINT `employee_department_department_id_fk` FOREIGN KEY (`department_id`) REFERENCES `department` (`department_id`))很明显插入的时候失败了。我寻找了一下原因，原来是插入数据的时候，外键的值在对应表的主键中不存在，所以插入失败。这个问题挺隐蔽的，积累经验啦。