比如，要获取1-9的随机数，如此调用即可：
select rand_num(1, 9);
mysql 定义function rand
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mysql 定义function rand
FUNCTION rand_num (
start_num INTEGER,
end_num INTEGER
) RETURNS INTEGER
BEGIN
RETURN FLOOR(start_num + RAND() * (end_num - start_num + 1));
END;