Need Help in tuning this query

Question

select CO_PROFILE.CO_NO AS "UEN No.",
CO_PROFILE.CO_NAME AS "Entity Name",
DECODE(CO_PROFILE.CO_TYPE,'A1','PUBLIC COMPANY LIMITED BY SHARES',
'A3','COMPANY LIMITED BY GUARANTEE',
'A4','UNLIMITED PUBLIC COMPANY',
'B1','LIMITED PRIVATE COMPANY',
'B2','LIMITED EXEMPT PRIVATE COMPANY',
'B3','UNLIMITED PRIVATE COMPANY',
'B4','UNLIMITED EXEMPT PRIVATE COMPANY',
'F1','FOREIGN COMPANY REGISTERED IN SINGAPORE') AS "Entity Type",
M_STATUS.STATUS_DESC AS "Entity Status",
PAYMENT_DETAIL.SERVICE_CODE AS "Service Code",
PAYMENT_DETAIL.PAYMENT_CODE AS "Payment Code",
CO_TRANS_MAST.CO_TRANS_ID AS "Transaction Type",
M_PAYMENT_CODE.PAYMENT_DESC AS "Payment Description",
M_PAYMENT_CODE.REVENUE_CODE AS "Revenue Account",
CO_TRANS_MAST.NUM AS "Number Of Transactions",
PAY_NEW.UNIT_AMT AS "Revenue Amount1",
PAY_NEW.FILING_AMT AS "Revenue Amount2",
PAYMENT_DETAIL.UNIT_FEE AS "Unit Cost"
from CO_PROFILE,
M_STATUS,
PAYMENT_DETAIL,
CO_TRANS_MASTER,
(Select COUNT(CO_NO) AS "NUM",CO_TRANS_ID,CO_NO
from CO_TRANS_MASTER
group by CO_NO,CO_TRANS_ID
)CO_TRANS_MAST,
(Select Sum(UNIT_FEE) AS UNIT_AMT,
  SUM(FILING_FEE) AS FILING_AMT,
   TRANS_NO AS TRANS_NO
  from
  PAYMENT_DETAIL
  group by
  TRANS_NO)
PAY_NEW,
M_PAYMENT_CODE
where rownum=1
and CO_PROFILE.CO_STATUS=M_STATUS.STATUS_CODE
and M_STATUS.TRANS_ID='COMP'
and CO_TRANS_MASTER.CO_TRANS_ID=CO_TRANS_MAST.CO_TRANS_ID
and CO_TRANS_MASTER.CO_NO=CO_TRANS_MAST.CO_NO
and PAYMENT_DETAIL.TRANS_NO=CO_TRANS_MASTER.CO_TRANS_NO
and PAY_NEW.TRANS_NO=PAYMENT_DETAIL.TRANS_NO
and CO_TRANS_MAST.CO_NO= CO_PROFILE.CO_NO
and M_PAYMENT_CODE.PAYMENT_CODE=PAYMENT_DETAIL.PAYMENT_CODE

Answer 1

Something seems wrong to me with the logical structure of the select.
1) You only get 1 row of output
but you
2) build sums for each trans_no
3) You join the table co_trans_master but at the same time you count over that one. Might be ok to do so, but it seems to be double the work.
Suggestion.
a) Build a select that joins the payment detail table. Then group this select and build the sums.
b) Add the count for the number of transactions to the select clause instead of and extra inline view in the from clause. Maybe as an analytical function if possible.