CREATE TABLE IF NOT EXISTS appointments (
  id                  INT AUTO_INCREMENT PRIMARY KEY,
  client_id           INT  NOT NULL,
  appointment_date    DATE NOT NULL,
  appointment_time    TIME NULL,
  appointment_type_id INT  NULL,
  note                TEXT NULL,
  created_by          INT  NULL,
  created_at          TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
  updated_at          TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  FOREIGN KEY (client_id)  REFERENCES clients(id) ON DELETE CASCADE,
  FOREIGN KEY (created_by) REFERENCES users(id)   ON DELETE SET NULL
);