mysql 외래키 foreign key 설정

 

 

ALTER TABLE `test_sch`.`practice_table` 
DROP COLUMN `status`,
ADD COLUMN `class_id` INT NULL AFTER `room`,
ADD INDEX `class_id_idx` (`class_id` ASC);
;
ALTER TABLE `test_sch`.`practice_table` 
ADD CONSTRAINT `fk_class_id`
  FOREIGN KEY (`class_id`)
  REFERENCES `test_sch`.`class_table` (`id`)
  ON DELETE CASCADE
  ON UPDATE SET NULL;