Get sql query result as json - sql

Question

I have a table test with two columns A and B and create table1 and table2 from it.
test table1 table2
A B A count(A) B count(B) A
95 1 95 7 1 3 95
5 11 5 2 11 2 5
95 1 9 4 95
95 9
95 1
95 9
5 11
95 9
95 9
How to get a result like:
{"node": [
{"child": [
{"value": 3,
"name": "1"},
{"value": 4,
"name": "9"}],
"value": 7,
"name": "95"},
{"child": [
{"value": 2,
"name": "11"}],
"value": 2,
"name": "5"}],
"name": "test",
"value": 9}
First I group by column A and count the groups name="95", value=7 and name="5", value=2. For each group I count also column B. There are alot of json functions, but till now I have no idea how to get the result above.
finely the query should be similar to:
select row_to_json(t) from ( select * , ( select array_to_json(array_agg(row_to_json(u))) from ( select * from table1 where table1.a=table2.a ) as u ) from table2 ) as t;

Answer 1

You can generate the correct json with a plpgsql function. This is not very difficult, although sometimes a little tedious. Check this one (rename tt to actual table name):
create or replace function test_to_json()
returns json language plpgsql
as $$
declare
rec1 record;
rec2 record;
res text;
begin
res = '{"node": [';
for rec1 in
select a, count(b) ct
from tt
group by 1
loop
res = format('%s{"child": [', res);
for rec2 in
select a, b, count(b) ct
from tt
where a = rec1.a
group by 1,2
loop
res = res || format('{"value": %s, "name": %s},', rec2.ct, rec2.b);
end loop;
res = rtrim(res, ',');
res = format('%s],"value": %s, "name": %s},', res, rec1.ct, rec1.a);
end loop;
res = rtrim(res, ',');
res = format('%s], "value": %s}', res, (select count(b) from tt));
return res:: json;
end $$;
select test_to_json();

Answer 2

Ugly but working and without plpgsql:
select json_build_object('node', json_agg(q3), 'name', 'test', 'value', (select count(1) from test))
from
(select json_agg(q2) from
(select a as name, sum(value) as value, json_agg(json_build_object('name', q1.name, 'value', q1.value)) as child
from
(select a, b as name, count(1) as value from test group by 1, 2) as q1
group by 1) as q2
) as q3;