delimiter $$
DROP PROCEDURE IF EXISTS `getID`$$
CREATE PROCEDURE getID(IN appID INT, IN tID INT, IN floor INT)
BEGIN
	DECLARE s VARCHAR(255);
	DECLARE f INT;
	SET f = floor - 1;
	SET @mID = 0;
	SET @ms=concat('SELECT `id` INTO @mID FROM `comment`  WHERE `appid`= ',appID,'
 AND `tid`= ',tID,' ORDER BY `id` LIMIT ',f,',1');
	PREPARE STMT FROM @ms;
	EXECUTE STMT;
END
$$
delimiter ;

delimiter $$
DROP PROCEDURE IF EXISTS `getID`$$
CREATE PROCEDURE getID(IN appID INT, IN tID INT, IN floor INT)
BEGIN
	DECLARE f INT;
	SET f = floor - 1;
	SET @appID = appID;
	SET @tID = tID;
	SET @f = f;
	SET @mID = 0;
	SET @ms = 'SELECT `id` INTO @mID FROM `wy_comment`  WHERE `appid`=?
 AND `tid`=? ORDER BY `id` LIMIT ?,1';
	PREPARE STMT FROM @ms;
	EXECUTE STMT USING @appID,@tID,@f;
END
$$
delimiter ;

CALL getID(25,3399,2);

SELECT @mID;