SQL Server 2022

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--Build data table
;WITH TABLE_1 AS ( --data
SELECT 1 T1_ID, 2 VAL UNION
SELECT 2 T1_ID, 4 VAL UNION
SELECT 3 T1_ID, 6 VAL UNION
SELECT 4 T1_ID, 8 VAL UNION
SELECT 5 T1_ID, 10 VAL
),
TABLE_2 AS ( --first level join
SELECT 1 T1_ID, 'AA' T2_ID UNION
SELECT 2 T1_ID, 'AA' T2_ID UNION
SELECT 3 T1_ID, 'BB' T2_ID UNION
SELECT 4 T1_ID, 'BB' T2_ID UNION
SELECT 5 T1_ID, 'BB' T2_ID
),
TABLE_3 AS ( --second level join
SELECT 1 T1_ID, 'CCC' T3_ID UNION
SELECT 2 T1_ID, 'CCC' T3_ID UNION
SELECT 3 T1_ID, 'CCC' T3_ID UNION
SELECT 4 T1_ID, 'CCC' T3_ID UNION
SELECT 5 T1_ID, 'CCC' T3_ID UNION
SELECT 1 T1_ID, 'DDD' T3_ID UNION
SELECT 2 T1_ID, 'DDD' T3_ID UNION
SELECT 3 T1_ID, 'DDD' T3_ID UNION
SELECT 4 T1_ID, 'DDD' T3_ID UNION
SELECT 5 T1_ID, 'DDD' T3_ID 
)

SELECT T2_ID, T3_ID, SUM(VAL) TOTAL
FROM TABLE_1 T1
JOIN (
    SELECT T1_ID, T2_ID FROM TABLE_2
    UNION ALL
    SELECT T1_ID, NULL FROM TABLE_1 -- Null fillers
) T2 ON T2.T1_ID = T1.T1_ID
JOIN (
    SELECT T1_ID, T3_ID FROM TABLE_3
    UNION ALL
    SELECT T1_ID, NULL FROM TABLE_1 -- Null fillers
) T3 ON T3.T1_ID = T1.T1_ID
GROUP BY T2_ID, T3_ID
ORDER BY
    CASE WHEN T2_ID IS NULL THEN 1 ELSE 2 END,
    CASE WHEN T3_ID IS NULL THEN 1 ELSE 2 END,
    T2_ID,
    T3_ID

T2_ID	T3_ID	TOTAL
null	null	30
null	CCC	30
null	DDD	30
AA	null	6
BB	null	24
AA	CCC	6
AA	DDD	6
BB	CCC	24
BB	DDD	24