Oracle SQL- Flag records based on record's date vs history

Question

This is my 1st post on the forum. Usually I was able to find what I needed - but to tell the truth - I am not really sure how to ask a correct question to the issue. Therefore,

Answer 1

You can achieve using row_number() function as below... modify as per your need...I assumed 2 years (means previous 24 months from sysdate ). You can run the sub-queries separately to check how its working.

Select 
"REGION"
,"COUNTRY"
,"IDNum"
,"CUSTOMER"
,"BUSSINESS"
,"FISCALYEARMONTH"
,"FISCALYEAR"
,"VALUE"
, ( case when ( TXNNO = 1 or TOTAL_TXN_LAST24MTH = 0 ) then 'New' else 'Existing' end ) as "HISTORICAL_PURCHASE_FLAG"  -- if no txn in last 24 month or its first txn then 'new' else 'existing'
from
(
  select 
  SubQry."REGION"
  , SubQry."COUNTRY"
  , SubQry."IDNum"
  , SubQry."CUSTOMER"
  , SubQry."BUSSINESS"
  , SubQry."FISCALYEARMONTH"
  , SUBQRY."FISCALYEAR"
  , SUBQRY."VALUE"
  , ROW_NUMBER() over (partition by SUBQRY."REGION",SUBQRY."COUNTRY",SUBQRY."IDNum",SUBQRY."CUSTOMER",SUBQRY."BUSSINESS" order by SUBQRY."FISCALYEARMONTH") as TXNNO,
  , SUM(case when (TO_NUMBER(TO_CHAR(sysdate,'YYYYMM')) - SUBQRY."FISCALYEARMONTH") < 24 then 1 else 0 end) as TOTAL_TXN_LAST24MTH
  From
  (
    SELECT
    T1."REGION"
    , T1."COUNTRY"
    , T1."IDNum"
    , T1."CUSTOMER"
    , T1."BUSSINESS"
    , T3."FISCALYEARMONTH"
    , T3."FISCALYEAR"
    , SUM(T4."VALUE") as VALUE
    FROM
    "DATABASE"."SALES" T4
    , "DATABASE"."CUSTOMER" T1
    , "DATABASE"."PRODUCT" T2
    , "DATABASE"."TIME" T3
    WHERE
    T4."CUSTOMERID" = T1."CUSTOMERID"
    AND T4."PRODUCTID" = T2."PRODUCTID"
    AND T4."DATEID" = T3."DATEID"
    AND T3."FISCALYEAR" IN ('2016')
    AND T1."COUNTRY" IN ('ENGLAND', 'France')
    GROUP BY
    T1."REGION"
    , T1."COUNTRY"
    , T1."IDNum"
    , T1."CUSTOMER"
    , T1."BUSSINESS"
    , T3."FISCALYEARMONTH"
    , T3."FISCALYEAR"
  ) SUBQRY
);