MySQL 随机生成各种类型的随机函数

DROP FUNCTION IF EXISTS rand_string;
delimiter //
CREATE FUNCTION rand_string(l_num tinyint UNSIGNED,l_type tinyint UNSIGNED)
RETURNS varchar(127)
BEGIN
-- Function : rand_string
-- Author : dbachina#dbachina.com
-- Date : 2010/5/30
-- l_num : The length of random string
-- l_type: The string type
-- 1.0-9
-- 2.a-z
-- 3.A-Z
-- 4.a-zA-Z
-- 5.0-9a-zA-Z
-- <for example> :
-- mysql> select rand_string(12,5) random_string;
-- +---------------+
-- | random_string |
-- +---------------+
-- | 3KzGJCUJUplw |
-- +---------------+
-- 1 row in set (0.00 sec)
DECLARE i int UNSIGNED DEFAULT 0;
DECLARE v_chars varchar(64) DEFAULT '0123456789';
DECLARE result varchar ( 255) DEFAULT '';

IF l_type = 1 THEN
SET v_chars = '0123456789';
ELSEIF l_type = 2 THEN
SET v_chars = 'abcdefghijklmnopqrstuvwxyz';
ELSEIF l_type = 3 THEN
SET v_chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
ELSEIF l_type = 4 THEN
SET v_chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
ELSEIF l_type = 5 THEN
SET v_chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
ELSE
SET v_chars = '0123456789';
END IF;

WHILE i < l_num DO
SET result = concat( result,substr(v_chars,ceil(rand()*(length(v_chars)-1)),1) );
SET i = i + 1;
END WHILE;
RETURN result;
END;
//
delimiter ;