Supplier Balance

Dear All,

I'm trying to find a query that retrieve the balance (account balance in the starting date  , ending balance at the end of the period ) a month for example

for  a specific supplier

I have this query that give  me the vendor id , name site code of a supplier but I'm not finding a way to retrieve the other requested values

query:

"

select distinct 
SUP.VENDOR_ID,
SUP.VENDOR_NAME,
SUP.SEGMENT1 VENDOR_NUMBER,
SUPA.VENDOR_SITE_CODE
from AP_SUPPLIERS SUP,
AP_SUPPLIER_SITES_ALL SUPA
where
SUP.VENDOR_ID = SUPA.VENDOR_ID
and SUP.SEGMENT1 =:vend_nb