sell_ids, Oracle - rextester

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with 
  table1(seq_id, req_id, call_id, sell_id, region, cnt) as (
    select 1, 123, 'C001', 'S1', 'AGL',               510563 from dual union all
    select 2, 123, 'C001', 'S1', 'USL',               122967 from dual union all
    select 3, 123, 'C001', 'S1', 'VALIC',             614106 from dual union all
    select 4, 123, 'C001', 'S2', 'Inforce',          1247636 from dual union all
    select 5, 123, 'C001', 'S2', 'NB',                     0 from dual union all
    select 6, 123, 'C001', 'S3', 'Seriatim Summary', 1247636 from dual ),
  t as (
      select sell_id sid, req_id, call_id, sum(cnt) cnt
        from table1 
        group by sell_id, req_id, call_id )
select case t1.sid when 'S1' then 1 when 'S2' then 2 when 'S3' then 3 end id, 
       t1.req_id, t1.call_id, t1.sid||'_vs_'||t2.sid call_id, t1.cnt - t2.cnt diff
  from t t1 
  join t t2 on t1.req_id = t2.req_id and t1.call_id = t2.call_id 
           and (t1.sid, t2.sid) in (('S1', 'S2'), ('S2', 'S3'), ('S3', 'S1'))
  order by id


absolute service time: 1,32 sec