mysql自定义函数random_str,产生随机字符串

delimiter $$
CREATE FUNCTION random_str(n int) RETURNS varchar(255) 
begin        
  declare chars_str varchar(100) 
  default "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
  declare return_str varchar(255) default "";        
  declare i int default 0;
  while i < n do        
      set return_str=concat(return_str,substring(chars_str,floor(1+rand()*52),1));
      set i= i+1;        
  end while;        
  return return_str;    
end $$
delimiter ;