mysql过程没有按预期执行

使用mysql 5.7,执行此过程时:

DELIMITER $$
CREATE PROCEDURE tres()
BEGIN
    DECLARE maxid INT;
    DECLARE x INT;
    SET maxid = 655;
    SET x=1;
    WHILE x<= maxid DO 
        INSERT INTO `forum_topicresponder` (topic_id, username, reply_id) SELECT p.topic_id, p.creator_name, p.id  FROM forum_post AS p  WHERE p.topic_id=x;
     SET  x = x + 1; 
     END WHILE;
END$$

我得到

mysql>调用tres();
查询正常,0行受影响(3.49秒)

但是,当我为循环范围内的特定值执行插入时:

 INSERT INTO `forum_topicresponder` (topic_id, username, reply_id) SELECT p.topic_id, p.creator_name, p.id  FROM forum_post AS p  WHERE p.topic_id=42;

我看到插入的结果没有问题。

表架构:

CREATE TABLE `forum_topicresponder` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `topic_id` int(10) NOT NULL DEFAULT '0',
  `username` varchar(300) CHARACTER SET utf8mb4 NOT NULL DEFAULT 'na',
  `reply_id` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=94 DEFAULT CHARSET=latin1;

和

CREATE TABLE `forum_post` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `body` varchar(16000) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  `topic_id` int(11) NOT NULL DEFAULT '0',
  `creator_id` int(11) NOT NULL DEFAULT '0',
  `creator_name` varchar(30) NOT NULL DEFAULT 'NA',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6264595 DEFAULT CHARSET=utf8;

那么这里有什么问题,我该怎么解决呢?