calcolare il saldo corrente nella query di Oracle

Penso che tu stia cercando:

SELECT   B.NO_KLAIM AS id,
         a.amount AS amount_a,
         B.AMOUNT AS amount_b,
         a.amount - SUM (B.AMOUNT) 
                   OVER (partition by b.no_klaim ORDER BY B.cp_id ROWS UNBOUNDED PRECEDING)
              AS running_balance
FROM      TRX_TITIPAN A
           JOIN
              TRX_KLAIM_TITIPAN B
           ON A.NO_RESI_TITIPAN = B.NO_RESI_TITIPAN