CREATE TABLE IF NOT EXISTS `workloads` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `teacher_id` int(11) NOT NULL,
  `subject_id` int(11) NOT NULL,
  `class_id` int(11) NOT NULL,
  `lessons_per_week` int(11) NOT NULL,
  `school_id` INT,
  PRIMARY KEY (`id`),
  KEY `teacher_id` (`teacher_id`),
  KEY `subject_id` (`subject_id`),
  KEY `class_id` (`class_id`),
  CONSTRAINT `workloads_ibfk_1` FOREIGN KEY (`teacher_id`) REFERENCES `teachers` (`id`),
  CONSTRAINT `workloads_ibfk_2` FOREIGN KEY (`subject_id`) REFERENCES `subjects` (`id`),
  CONSTRAINT `workloads_ibfk_3` FOREIGN KEY (`class_id`) REFERENCES `classes` (`id`),
  CONSTRAINT `fk_workloads_school_id` FOREIGN KEY (`school_id`) REFERENCES `schools`(`id`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;