set global log_bin_trust_function_creators = 1;
DROP FUNCTION IF EXISTS rand_string;
DELIMITER $$
CREATE FUNCTION rand_string(n INT)
RETURNS VARCHAR(255)
BEGIN
DECLARE chars_str varchar(100) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
DECLARE return_str varchar(255) DEFAULT '';
DECLARE i INT DEFAULT 0;
WHILE i < n DO
SET return_str = concat(return_str,substring(chars_str , FLOOR(1 + RAND()*62 ),1));
SET i = i +1;
END WHILE;
RETURN return_str;
END $$
DELIMITER ;
经测试，函数创建后与当前数据库绑定，下面语句可以查看函数相关信息。
SHOW FUNCTION STATUS WHERE Db='database_name';