我有一个过程，通过迭代地向id值添加一个随机数，手动递增id。有时这会导致id不递增，即使我可以确认 (FLOOR(RAND()*(1000-2+1))+2) 始终返回2-1000之间的值。但以下是简单的陈述：

SET `nextid` = `nextid` + (FLOOR(RAND()*(1000-2+1))+2);

仍然无法增加 nextid 不时地。如果我分开我的 (FLOOR(RAND()*(1000-2+1))+2) 将值放入一个单独的变量中，并将这两个变量相加，这样就不会发生这种情况。下面是一个再现行为的最小示例测试用例。

DELIMITER $$
CREATE PROCEDURE `test`()
BEGIN
    DECLARE `nextid` BIGINT DEFAULT 793991813529600000;
    DECLARE `previous` BIGINT DEFAULT 0;
    DECLARE `i` BIGINT DEFAULT 0;
    DECLARE `random` BIGINT DEFAULT 0;

    WHILE `i` < 100000 DO
        SET `previous` = `nextid`;
        -- Produce a random number between 2 and 1000.
        SET `random` = (FLOOR(RAND()*(1000-2+1))+2);
        SET `nextid` = `nextid` + `random`;

        -- Error if the nextid is no different from the previous ID.
        -- This is successful every time. 
        IF `nextid` = `previous` THEN
            SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Oh no!', MYSQL_ERRNO = 2000;
        END IF;

        SET `i` = `i` + 1;
    END WHILE;

    SET `i` = 0;
    WHILE `i` < 100000 DO
        SET `previous` = `nextid`;
        -- Increment the ID by a random number and do the set in a single statment.
        SET `nextid` = `nextid` + (FLOOR(RAND()*(1000-2+1))+2);

        -- This fails randomly, but reliably.
        IF `nextid` = `previous` THEN
            SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Whoops!', MYSQL_ERRNO = 2000;
        END IF;

        SET `i` = `i` + 1;
    END WHILE;

END $$
DELIMITER ;

CALL `test`();
DROP PROCEDURE IF EXISTS `test`;

看起来这可能是一些铸造问题，但我找不到任何东西来证实。所以我的问题是，是什么导致了这种行为？
其他细节；

mysql --version
mysql  Ver 14.14 Distrib 5.7.24, for Linux (x86_64) using  EditLine wrapper