i want to add column and show when we have same item and customer type

select item.name, bh.customer_type, bl.quantity from tbl_item_master item, tbl_billing_header bh, tbl_billing_line bl where item.name = bl.item_name and bh.bill_no=bl.bill_no and bh.bill_status="B"


*OutPut*
item    customertype  quantity
Heart   W             120
LIVER   W             121
WINGSML I             11
Heart   W             200

i want to add column and show when we have same item and customer type suppose when Item which is heart has same customer type that is W then in that case we will add quantity to 220 and show it