CREATE TABLE messages(
  msg_id    INT         NOT NULL PRIMARY KEY AUTO_INCREMENT,
  parent_id INT         NOT NULL,
  status    VARCHAR(3)  NOT NULL,
  from_who  VARCHAR(30) NOT NULL,
  to_who    VARCHAR(30) NOT NULL,
  sent_when DATETIME    NOT NULL,
  msg_text  TEXT        NOT NULL
);

CREATE TABLE users(
  user      VARCHAR(30) NOT NULL PRIMARY KEY,
  # etc, etc.
);