ALTER TABLE career_plan
  ADD group_id BIGINT  AFTER name,
  ADD INDEX group_id_idx (group_id)
;
CREATE TABLE career_plan_group (
  id BIGINT AUTO_INCREMENT,
  name VARCHAR(255),
  PRIMARY KEY(id)
) ENGINE = INNODB;

ALTER TABLE career_plan
  ADD CONSTRAINT career_plan_group_id_career_plan_group_id FOREIGN KEY (group_id) REFERENCES career_plan_group(id) ON DELETE SET NULL
;