MySQL：我应该使用哪种约束来使用户不能对自己的消息进行投票？

Question

用户有消息，投票有消息和用户。我想这样做，以便用户不能对自己的消息进行投票。我不知道如何创建此SQL约束。我可以使用什么MySQL约束来使用户无法对自己的消息进行投票？

DROP DATABASE IF EXISTS uncovery;
CREATE DATABASE uncovery;

SET foreign_key_checks=0;

USE uncovery;

CREATE TABLE marks (
  id int(5) AUTO_INCREMENT,
  PRIMARY KEY (id),
  x float(10, 6) NOT NULL,
  y float(10, 6) NOT NULL,
  z float(10, 6) NOT NULL,
  timestamp timestamp DEFAULT CURRENT_TIMESTAMP,
  messageId int(5) NULL,
  commentId int(5) NULL,
  userToken VARCHAR(255),
  FOREIGN KEY (messageId) REFERENCES messages(id),
  FOREIGN KEY (commentId) REFERENCES comments(id),
  FOREIGN KEY (userToken) REFERENCES users(token)
);

CREATE TABLE messages (
  id int(5) AUTO_INCREMENT,
  userToken VARCHAR(255),
  messageString text NOT NULL,
  image VARCHAR(255),
  score int(5) DEFAULT 0,
  PRIMARY KEY (id)
);

CREATE TABLE comments (
  id int(5) AUTO_INCREMENT,
  commentString text NOT NULL,
  messageId int(5),
  PRIMARY KEY (id),
  FOREIGN KEY (messageId) REFERENCES messages(id)
);

CREATE TABLE votes (
  id int(5) AUTO_INCREMENT,
  PRIMARY KEY(id),
  userToken VARCHAR(255) NOT NULL,
  messageId int(5) NULL,
  commentId int(5) NULL,
  FOREIGN KEY (userToken) REFERENCES users(token),
  FOREIGN KEY (messageId) REFERENCES messages(id),
  FOREIGN KEY (commentId) REFERENCES comments(id),
  UNIQUE KEY (userToken, messageId),
  UNIQUE KEY (userToken, commentId)
);

CREATE TABLE users (
  token VARCHAR(255),
  PRIMARY KEY(token),
  total_votes int(5) DEFAULT 0
);

-- If a message does not have a userToken then this will not work
DELIMITER //
CREATE TRIGGER vote_increment AFTER INSERT ON votes
FOR EACH ROW
  BEGIN
    UPDATE users SET users.total_votes = (users.total_votes + 1) WHERE users.token = 
      (SELECT userToken FROM messages WHERE id = NEW.messageId);
  END;//
DELIMITER ;