Oracle 21c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
 CREATE TABLE t1 (gdu, amount) AS
  SELECT 'A' ,   100 FROM DUAL UNION ALL
  SELECT 'B' ,   150 FROM DUAL UNION ALL
  SELECT 'C' ,   125 FROM DUAL UNION ALL
  SELECT 'A1',   500 FROM DUAL UNION ALL
  SELECT 'B1',   800 FROM DUAL UNION ALL
  SELECT 'B2', 15000 FROM DUAL UNION ALL
  SELECT 'C2', 10000 FROM DUAL;
7 rows affected

CREATE TABLE t2 (g, d, u) AS
  SELECT 'A', 'A1', null FROM DUAL UNION ALL
  SELECT 'B', 'B1', 'B2' FROM DUAL UNION ALL
  SELECT 'C', 'C1', 'C2' FROM DUAL;
3 rows affected

SELECT t1.gdu,
       CASE t1.gdu WHEN t2.g THEN t2.g END AS g,
       CASE t1.gdu WHEN t2.d THEN t2.d END AS d,
       CASE t1.gdu WHEN t2.u THEN t2.u END AS u,
       t1.amount
FROM   t1
       INNER JOIN t2
       ON (t1.gdu = t2.g OR t1.gdu = t2.d OR t1.gdu = t2.u)
ORDER BY g, d, u


GDU
G
D
U
AMOUNT


A
A
null
null
100

B
B
null
null
150

C
C
null
null
125

A1
null
A1
null
500

B1
null
B1
null
800

B2
null
null
B2
15000

C2
null
null
C2
10000

GDU	G	D	U	AMOUNT
A	A	null	null	100
B	B	null	null	150
C	C	null	null	125
A1	null	A1	null	500
B1	null	B1	null	800
B2	null	null	B2	15000
C2	null	null	C2	10000