mysql 저장 프로세스에서 임의로 문자열 생성

#       ，       
drop procedure if exists  randstr;
delimiter $$
create procedure  randstr(num int(11))     #                       ，              test_randstr;
    begin
    declare str char(255)  default 'q1we23r4t5y6u7i8o9p0asdfghjklzxcvbnm';
    declare nums int(11);
    declare returnstr char(255);                    #SQL          
    declare i int(11) default  0;                   #          begin    ， begin        
    select floor(truncate(rand(),1)*36)+1 into nums;   # 1            0   
    select substring(str,nums,1)  into returnstr;
    #declare i int(11) default  0;                  #          begin    ， begin        ，          
    while  i <num do
    select floor(truncate(rand(),1)*36)+1 into nums;
    select concat(substring(str,nums,1),returnstr) into returnstr;
    #set returnstr=concat(substring(str,nums,1),returnstr);
    set i=i+1;
    end while;
    select returnstr as randstr;
    end
    $$
    delimiter ;
call randstr(5);