msyql组内排序

select ORDER_CODE,PO_ROW_NUM , cum_delivery_rate,
           @num:=if(@str=CONCAT(ORDER_CODE,PO_ROW_NUM),@num+1,1) as num,
 @str:=CONCAT(ORDER_CODE,PO_ROW_NUM) str
   from app_pur_cycle_fact a,(SELECT @str := '', @num :=0) q
   where PO_Start_Date>='2019-03-01'
   and PO_Start_Date<='2020-03-10'