SQL Purchase

The script below links pos to invoices but I cannot get the purchase order contract number even though I have requested it from the PO_LINES_ALL table. Does someone have an idea how I can get the contract number into the script. ?

SELECT   A.ORG_ID "ORG ID",

         E.VENDOR_NAME "VENDOR NAME",

         UPPER (E.VENDOR_TYPE_LOOKUP_CODE) "VENDOR TYPE",

         F.VENDOR_SITE_CODE "VENDOR SITE",

         F.ADDRESS_LINE1 "ADDRESS",

         F.CITY "CITY",

         F.COUNTRY "COUNTRY",

         TO_CHAR (TRUNC (D.CREATION_DATE)) "PO DATE",

        G.CONTRACT_NUM "CONTRACT NUM",

         D.SEGMENT1 "PO NUMBER",

         D.TYPE_LOOKUP_CODE "PO TYPE",