ID_ISIN   QUOTE_CRNY   DESCR           RATIO              ALLOCATIONASSETTYPE
L000123    USD              O              0.0769          Other total
L000129    USD              O              0.0669          Other total
D123458    USD              O              0.64039         Other total
M123456    USD              O              5.64039         Other total
F563458    USD              C              0.84039         Other total
G123456    USD              null           0.04039         Other total
L000123    USD              C              5.0769          Other total

CREATE VIEW v_combined_data AS
WITH combined_data
AS
(
SELECT t1.fund_isin
      ,t1.fund_quote_crny
      ,t1.member_descr
      ,t1.member_ratio
      ,t1.allocationassettype
      ,t2.fund_isin fund_isin_tst
      ,t2.fund_quote_crny fund_quote_crny_tst
      ,t2.member_descr member_descr_tst
      ,t2.member_ratio member_ratio_tst
      ,t2.allocationassettype allocationassettype_tst
FROM   is_id t1
FULL   OUTER JOIN is_id_tst t2
ON     t1.fund_isin = t2.fund_isin
AND    t1.fund_quote_crny = t2.fund_quote_crny
AND    t1.member_descr = t2.member_descr
)
-- for member_descr = 'O' and for common fund_isin field value from both tables, 
-- check the member_ratio field and take only the row where member_ratio field value is low.
SELECT d.fund_isin
      ,d.fund_quote_crny
      ,d.member_descr
      ,LEAST(d.member_ratio,d.member_ratio_tst) member_ratio
      ,d.allocationassettype
  FROM combined_data d
WHERE d.member_descr = 'O'
  AND d.fund_isin IS NOT NULL 
  AND d.fund_isin_tst IS NOT NULL
UNION ALL
--for member_descr = 'O' and if the fund_isin exist in one table but not in another then take those rows(bidirectional)
--exists in IS_ID and not in IS_ID_TST
SELECT d.fund_isin
      ,d.fund_quote_crny
      ,d.member_descr
      ,d.member_ratio
      ,d.allocationassettype
  FROM combined_data d
WHERE d.member_descr = 'O'
  AND NOT EXISTS (SELECT 1
                    FROM combined_data ci
                   WHERE ci.fund_isin_tst = d.fund_isin
                     AND ci.fund_quote_crny_tst = d.fund_quote_crny
                     AND ci.member_descr_tst = 'O')
UNION ALL
--for member_descr = 'O' and if the fund_isin exist in one table but not in another then take those rows(bidirectional)
--exists in IS_ID_TST and not in IS_ID
SELECT d.fund_isin_tst
      ,d.fund_quote_crny_tst
      ,d.member_descr_tst
      ,d.member_ratio_tst
      ,d.allocationassettype_tst
  FROM combined_data d
WHERE d.member_descr_tst = 'O'
  AND NOT EXISTS (SELECT 1
                    FROM combined_data ci
                   WHERE ci.fund_isin = d.fund_isin_tst
                     AND ci.fund_quote_crny = d.fund_quote_crny_tst
                     AND ci.member_descr = 'O')
UNION ALL
--for all the rows where member_descr ! = 'O', take all those rows from table IS_ID_TST
SELECT d.fund_isin_tst
      ,d.fund_quote_crny_tst
      ,d.member_descr_tst
      ,d.member_ratio_tst
      ,d.allocationassettype_tst
  FROM combined_data d
WHERE d.fund_isin_tst IS NOT NULL
  AND (d.member_descr_tst != 'O' OR d.member_descr_tst IS NULL);