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 --  :-- 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 THENSET v_chars = '0123456789';ELSEIF l_type = 2 THENSET v_chars = 'abcdefghijklmnopqrstuvwxyz';ELSEIF l_type = 3 THENSET v_chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';ELSEIF l_type = 4 THENSET v_chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';ELSEIF l_type = 5 THENSET v_chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';ELSESET v_chars = '0123456789';END IF;WHILE i < l_num DOSET result = concat( result,substr(v_chars,ceil(rand()*(length(v_chars)-1)),1) );SET i = i + 1;END WHILE;RETURN result;END;//delimiter ;

转自http://www.dbachina.com/2010/05/31/mysql_random_string_function/