DB2 Building json using JSON_ARRAY - db2

Question

I am using DB2LUW 11.5.
I am building a JSON under usage of the below tables and want an output like this
I tried many things but I come not up to a solution.
{
"ID": 1,
"NAME": "a",
"B_OBJECTS": [{
"ID": 1,
"SIZE": 5
}, {
"ID": 2,
"SIZE": 10
}, {
"ID": 3,
"SIZE": 15
}
],
"C_OBJECTS": [{
"ID": 1,
"SIZE": 100
}, {
"ID": 2,
"SIZE": 200
}
]
}
Table_A
ID
NAME
1
a
Table_B
ID
ID_A
SIZE
1
1
5
2
1
10
3
1
15
Table_C
ID
ID_A
SIZE
1
1
100
2
1
200
WITH
TABLE_A(ID,NAME) AS
(
VALUES (1, 'a')
)
, TABLE_B(ID, ID_A, SIZE) AS
(
VALUES (1, 1, 5), (2, 1, 10), (3, 1, 15)
), TABLE_C(ID, ID_A, SIZE) AS
(
VALUES (1, 1, 100), (2,1, 200)
)
, JSON_STEP_1 AS
(
SELECT A_ID, A_NAME, B_ID, C_ID
, JSON_OBJECT('ID' VALUE B_ID, 'SIZE' VALUE B_SIZE) B_JSON
, JSON_OBJECT('ID' VALUE C_ID, 'SIZE' VALUE C_SIZE) C_JSON
FROM
(
SELECT
A.ID AS A_ID, A.NAME AS A_NAME, B.ID AS B_ID, B.SIZE AS B_SIZE, C.ID AS C_ID, C.SIZE AS C_SIZE
FROM TABLE_A A
JOIN TABLE_B B ON B.ID_A = A.ID
JOIN TABLE_C C ON C.ID_A = A.ID
)
GROUP BY A_ID, A_NAME, B_ID, B_SIZE, B_ID, B_SIZE, C_ID, C_SIZE
)
, JSON_STEP_2 AS
(
SELECT
JSON_OBJECT
(
'ID' VALUE A_ID,
'NAME' VALUE A_NAME,
'B_OBJECTS' VALUE JSON_ARRAY (LISTAGG(B_JSON, ', ') WITHIN GROUP (ORDER BY B_ID) FORMAT JSON) FORMAT JSON,
'C_OBJECTS' VALUE JSON_ARRAY (LISTAGG(C_JSON, ', ') WITHIN GROUP (ORDER BY C_ID) FORMAT JSON) FORMAT JSON
) JSON_OBJS
FROM JSON_STEP_1
GROUP BY A_ID, A_NAME
)
SELECT * FROM JSON_STEP_2
I get a mulitplication of the results
{
"ID": 1,
"NAME": "a",
"B_OBJECTS": [{
"ID": 1,
"SIZE": 5
}, {
"ID": 1,
"SIZE": 5
}, {
"ID": 2,
"SIZE": 10
}, {
"ID": 2,
"SIZE": 10
}, {
"ID": 3,
"SIZE": 15
}, {
"ID": 3,
"SIZE": 15
}
],
"C_OBJECTS": [{
"ID": 1,
"SIZE": 100
}, {
"ID": 1,
"SIZE": 100
}, {
"ID": 1,
"SIZE": 100
}, {
"ID": 2,
"SIZE": 200
}, {
"ID": 2,
"SIZE": 200
}, {
"ID": 2,
"SIZE": 200
}
]
}

Answer 1

You have to build arrays from table B and C in different queries.
By the way, since your version is 11.5 you will maybe sometime have JSON_ARRAYAGG available
So you can write :
WITH
TABLE_A(ID,NAME) AS
(
VALUES (1, 'a')
)
, TABLE_B(ID, ID_A, SIZE) AS
(
VALUES (1, 1, 5), (2, 1, 10), (3, 1, 15)
), TABLE_C(ID, ID_A, SIZE) AS
(
VALUES (1, 1, 100), (2,1, 200)
)
select
JSON_OBJECT
(
'ID' VALUE A.ID,
'NAME' VALUE A.NAME,
'B_OBJECTS' VALUE (
select json_arrayagg(
JSON_OBJECT('ID' VALUE b.ID, 'SIZE' VALUE b.SIZE)
) from table_b b where b.id_a = a.id
) format json,
'C_OBJECTS' VALUE (
select json_arrayagg(
JSON_OBJECT('ID' VALUE C.ID, 'SIZE' VALUE C.SIZE)
) from table_c c where c.id_a = a.id) format json
absent on null
)
from table_a a
gives
{
"ID": 1,
"NAME": "a",
"B_OBJECTS": [{
"ID": 1,
"SIZE": 5
}, {
"ID": 2,
"SIZE": 10
}, {
"ID": 3,
"SIZE": 15
}
],
"C_OBJECTS": [{
"ID": 1,
"SIZE": 100
}, {
"ID": 2,
"SIZE": 200
}
]
}