demo, Sql Server - rextester

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--Sql Server 2014 Express Edition
--Batches are separated by 'go'

WITH yourTable AS (
    SELECT '2017-07-01' AS Date, 'DEPA1' AS AccNum, 'HKGCIFSRCKEY002DEPA1SGD' AS ID, 1000 AS Balance, 'SGD' AS Curncy, 0 AS Interest, 'Open' AS Description UNION ALL
    SELECT '2017-08-01', 'DEPA1', 'HKGCIFSRCKEY002DEPA1SGD', 1010,  'SGD', 10,  'Open'    UNION ALL
    SELECT '2017-09-01', 'DEPA1', 'HKGCIFSRCKEY002DEPA1SGD', 1020,  'SGD', 10,  'Closed'  UNION ALL
    SELECT '2017-06-01', 'DEPA2', 'HKGCIFSRCKEY002DEPA2SGD', 10000, 'SGD', 0,   'Open'    UNION ALL
    SELECT '2017-07-01', 'DEPA2', 'HKGCIFSRCKEY002DEPA2SGD', 10100, 'SGD', 100, 'Open'    UNION ALL
    SELECT '2017-08-01', 'DEPA2', 'HKGCIFSRCKEY002DEPA2SGD', 10200, 'SGD', 100, 'Open'    UNION ALL
    SELECT '2017-09-01', 'DEPA2', 'HKGCIFSRCKEY002DEPA2SGD', 10300, 'SGD', 100, 'Dormant'
)

SELECT
    t.Date, t.AccNum, t.ID, t.Balance, t.Curncy, t.Interest, t.Description
FROM
(
    SELECT Date, AccNum, ID, Balance, Curncy, Description,
        SUM(Interest) OVER (PARTITION BY AccNum) AS Interest,
        RANK() OVER (PARTITION BY AccNum ORDER BY Date DESC) rank
    FROM yourTable
) t
WHERE t.rank = 1;

View schema
Execution time: 0 sec, rows selected: 2, rows affected: 0, absolute service time: 0,14 sec