PostgreSQL query on Json having nested Array - postgresql

Question

I have below json data stored in Postgres DB with column as json:
{"users": [
{
"id": 1,
"data": [
{
"pos": "BA",
"endDate": "2022-07-31",
"startDate": "2022-01-01"
},
{
"pos": "BA2",
"endDate": "2022-09-30",
"startDate": "2022-08-01"
},
{
"pos": "BA3",
"endDate": "2023-03-31",
"startDate": "2022-10-01"
},
{
"pos": "BA4",
"endDate": "2023-06-08",
"startDate": "2023-04-01"
}
]
},
{
"id": 2,
"data": [
{
"pos": "BA",
"endDate": "2022-07-31",
"startDate": "2022-01-01"
},
{
"pos": "BA2",
"endDate": "2022-09-30",
"startDate": "2022-08-01"
},
{
"pos": "BA3",
"endDate": "2023-03-31",
"startDate": "2022-10-01"
},
{
"pos": "BA4",
"endDate": "2023-06-08",
"startDate": "2023-04-01"
}
]
},
{
"id": 3,
"data": [
{
"pos": "BA",
"endDate": "2022-07-31",
"startDate": "2022-01-01"
},
{
"pos": "BA2",
"endDate": "2022-09-30",
"startDate": "2022-08-01"
},
{
"pos": "BA3",
"endDate": "2023-03-31",
"startDate": "2022-10-01"
},
{
"pos": "BA4",
"endDate": "2023-06-08",
"startDate": "2023-04-01"
}
]
}
]
}
I need to write a query to filter the data based on the startDate and endDate.
So if the startDate is 2022-01-01 and endDate is 2022-12-31 then query should return below json:
{"users": [
{
"id": 1,
"data": [
{
"pos": "BA",
"endDate": "2022-07-31",
"startDate": "2022-01-01"
},
{
"pos": "BA2",
"endDate": "2022-09-30",
"startDate": "2022-08-01"
}
]
},
{
"id": 2,
"data": [
{
"pos": "BA",
"endDate": "2022-07-31",
"startDate": "2022-01-01"
},
{
"pos": "BA2",
"endDate": "2022-09-30",
"startDate": "2022-08-01"
}
]
},
{
"id": 3,
"data": [
{
"pos": "BA",
"endDate": "2022-07-31",
"startDate": "2022-01-01"
},
{
"pos": "BA2",
"endDate": "2022-09-30",
"startDate": "2022-08-01"
}
]
}
]
}
Can someone help me with the query ?

Answer 1

Well, this is a bit complicated. Inside-out, first flatten the JSON field then filter and finally re-aggregate into a JSON object again. Please note however that it is worth reviewing the data design. A normalized one would make things way better and easier. Please also note that it is extremely difficult to maintain data quality and consistency in a complex composite JSON field while supported out-of-the-box in a proper normalized model.
select json_build_object('users', json_agg(t))
from
(
select jvalue ->> 'id' as id, json_agg(j) as data
from
json_array_elements
(
'{"users":[
{"id":1,"data":[{"pos":"BA","endDate":"2022-07-31","startDate":"2022-01-01"},{"pos":"BA2","endDate":"2022-09-30","startDate":"2022-08-01"},{"pos":"BA3","endDate":"2023-03-31","startDate":"2022-10-01"},{"pos":"BA4","endDate":"2023-06-08","startDate":"2023-04-01"}]},
{"id":2,"data":[{"pos":"BA","endDate":"2022-07-31","startDate":"2022-01-01"},{"pos":"BA2","endDate":"2022-09-30","startDate":"2022-08-01"},{"pos":"BA3","endDate":"2023-03-31","startDate":"2022-10-01"},{"pos":"BA4","endDate":"2023-06-08","startDate":"2023-04-01"}]},
{"id":3,"data":[{"pos":"BA","endDate":"2022-07-31","startDate":"2022-01-01"},{"pos":"BA2","endDate":"2022-09-30","startDate":"2022-08-01"},{"pos":"BA3","endDate":"2023-03-31","startDate":"2022-10-01"},{"pos":"BA4","endDate":"2023-06-08","startDate":"2023-04-01"}]}
]}'::json -> 'users'
) as jvalue
cross join lateral json_array_elements(jvalue -> 'data') as j(value_object)
where (value_object ->> 'startDate')::date >= '2022-01-01'
and (value_object ->> 'endDate')::date <= '2022-12-31'
group by id
) as t;