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', 'AB', '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', 'DB', 'col_amount' FROM DUAL;
7 rows affected

SELECT 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
)


COLUMN_A
COLUMN_B
COLUMN_C


01
AB
col_amount

null
null
col_amount

null
null
col_amount

02
OA
col_amount

03
OE
col_amount

null
null
col_amount

04
DB
col_amount

COLUMN_A	COLUMN_B	COLUMN_C
01	AB	col_amount
null	null	col_amount
null	null	col_amount
02	OA	col_amount
03	OE	col_amount
null	null	col_amount
04	DB	col_amount