CREATE TABLE IF NOT EXISTS attendance (
  id INT UNSIGNED NOT NULL AUTO_INCREMENT,
  user_id INT UNSIGNED NOT NULL,
  work_date DATE NOT NULL,
  check_in_at DATETIME NOT NULL,
  check_out_at DATETIME NULL,
  created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (id),
  UNIQUE KEY uniq_attendance_user_day (user_id, work_date),
  CONSTRAINT fk_attendance_user FOREIGN KEY (user_id) REFERENCES users (id)
);