Generate a sequence in mysql -

i want enter value/sequence mysql field automatically. here sequence:

2342/abc/2013/08/01 

the last 1 sequence 01, 02, 03, , on.

the rule when month changes in above month 08 when 09 want start sequence again 01, 02 , on.

i have table table1(id,user_name,sq_number)

i use this

insert table1('user_name') values('bill') 

it insert sequence automatically

use before insert trigger, (below create sequence current date), add logic (it's not clear me).

create trigger insert_processor before insert on table1 each row begin set new.sq_number = concat('2342','/','abc','/', date_format(now(),'%y/%m/%d'));  end$$ 

if need unique sequence it's practice create table , use select in trigger.