Oracle 21c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
CREATE TABLE table_name (Column_A, Column_B, Column_C) AS
SELECT '01', 'AB', 'col_amount' FROM DUAL UNION ALL
SELECT '01', 'AB', 'col_amount' FROM DUAL UNION ALL
SELECT '01', 'AC', 'col_amount' FROM DUAL UNION ALL
SELECT '02', 'OA', 'col_amount' FROM DUAL UNION ALL
SELECT '03', 'OE', 'col_amount' FROM DUAL UNION ALL
SELECT '03', 'OE', 'col_amount' FROM DUAL UNION ALL
SELECT '04', 'OE', 'col_amount' FROM DUAL UNION ALL
SELECT '04', 'XX', 'col_amount' FROM DUAL;
8 rows affected

SELECT CASE b_rn WHEN 1 THEN DENSE_RANK() OVER (ORDER BY column_a, column_b) END
         AS no,
       CASE a_rn WHEN 1 THEN column_a END AS column_a,
       CASE b_rn WHEN 1 THEN column_b END AS column_b,
       column_c
FROM   (
  SELECT column_a,
         column_b,
         column_c,
         ROW_NUMBER() OVER (PARTITION BY column_a ORDER BY column_b, column_c)
           AS a_rn,
         ROW_NUMBER() OVER (PARTITION BY column_a, column_b ORDER BY column_c)
           AS b_rn
  FROM   table_name
)


NO
COLUMN_A
COLUMN_B
COLUMN_C


1
01
AB
col_amount

null
null
null
col_amount

2
null
AC
col_amount

3
02
OA
col_amount

4
03
OE
col_amount

null
null
null
col_amount

5
04
OE
col_amount

6
null
XX
col_amount


SELECT CASE a_rn WHEN 1 THEN DENSE_RANK() OVER (ORDER BY column_a) END
         AS no,
       CASE a_rn WHEN 1 THEN column_a END AS column_a,
       CASE b_rn WHEN 1 THEN column_b END AS column_b,
       column_c
FROM   (
  SELECT column_a,
         column_b,
         column_c,
         ROW_NUMBER() OVER (PARTITION BY column_a ORDER BY column_b, column_c)
           AS a_rn,
         ROW_NUMBER() OVER (PARTITION BY column_a, column_b ORDER BY column_c)
           AS b_rn
  FROM   table_name
)


NO
COLUMN_A
COLUMN_B
COLUMN_C


1
01
AB
col_amount

null
null
null
col_amount

null
null
AC
col_amount

2
02
OA
col_amount

3
03
OE
col_amount

null
null
null
col_amount

4
04
OE
col_amount

null
null
XX
col_amount

NO	COLUMN_A	COLUMN_B	COLUMN_C
1	01	AB	col_amount
null	null	null	col_amount
2	null	AC	col_amount
3	02	OA	col_amount
4	03	OE	col_amount
null	null	null	col_amount
5	04	OE	col_amount
6	null	XX	col_amount