Oracle 11g Release 2

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WITH TEST_TBL AS (
    SELECT 1 AS SL_NO, 234 AS ACC_NO, 'UNIP' AS ACC_NAME FROM dual UNION ALL
    SELECT 2,  234, 'UNIP' FROM dual UNION ALL
    SELECT 3,  234, 'UNIP' FROM dual UNION ALL
    SELECT 4,  256, 'PURP' FROM dual UNION ALL
    SELECT 5,  256, 'PURP' FROM dual UNION ALL
    SELECT 6,  289, 'KFAR' FROM dual UNION ALL
    SELECT 7,  210, 'FHAS' FROM dual UNION ALL
    SELECT 8,  210, 'FHAS' FROM dual UNION ALL
    SELECT 9,  210, 'FHAS' FROM dual UNION ALL
    SELECT 10, 110, 'PURP' FROM dual UNION ALL
    SELECT 11, 110, 'PURP' FROM dual UNION ALL
    SELECT 12, 110, 'PURP' FROM dual UNION ALL
    SELECT 13, 110, 'PURP' FROM dual
),
cte AS (
    SELECT
        SL_NO, 
        ACC_NO, 
        ACC_NAME,
        ROW_NUMBER() OVER(PARTITION BY ACC_NO, ACC_NAME ORDER BY SL_NO) RN,
        MIN(SL_NO) OVER (PARTITION BY ACC_NO, ACC_NAME) AS SL_NO_MIN
    FROM TEST_TBL A
)

SELECT
    SL_NO, 
    ACC_NO, 
    ACC_NAME,
    DENSE_RANK() OVER (ORDER BY SL_NO_MIN) AS DRN,
    RN
FROM cte
ORDER BY
    SL_NO;

SL_NO	ACC_NO	ACC_NAME	DRN	RN
1	234	UNIP	1	1
2	234	UNIP	1	2
3	234	UNIP	1	3
4	256	PURP	2	1
5	256	PURP	2	2
6	289	KFAR	3	1
7	210	FHAS	4	1
8	210	FHAS	4	2
9	210	FHAS	4	3
10	110	PURP	5	1
11	110	PURP	5	2
12	110	PURP	5	3
13	110	PURP	5	4