Create nested json blobs in PostgreSQL - sql

Question

I'm trying to create a nested json from a table like this:
+----------+---------+------------------------------+
| unixtime | assetid | data |
+----------+---------+------------------------------+
| 10 | 80 | {"inflow": 10, "outflow": 2} |
| 20 | 90 | {"inflow": 10, "outflow": 2} |
| 10 | 80 | {"inflow": 10, "outflow": 2} |
| 20 | 90 | {"inflow": 10, "outflow": 2} |
+----------+---------+------------------------------+
and get something like this:
{
"10": {
"80": {"inflow": 10, "outflow": 2},
"90": {"inflow": 10, "outflow": 2}
},
"20": {
"80": {"inflow": 10, "outflow": 2},
"90": {"inflow": 10, "outflow": 2}
}
}
I've tried recursively converting the json data to text, array_agg then convert the result to json blob using json_object, but that eventually screwed up the json structure with escape slashes ( \ ).
Any help would be appreciated
Here's the link to the data:
https://dbfiddle.uk/?rdbms=postgres_11&fiddle=26734e87d4b9aea4ceded4e414acec4c
Thank you.

Answer 1

You can use json_object_agg() function:
....
, m as (
select
unixdatetime,
assetid,
json_object(array_agg(description), array_agg(value::text))
as value
from input_data
group by unixdatetime, assetid
), j as
(
select json_object_agg("assetid","value") as js,m."unixdatetime"
from m
group by "unixdatetime"
)
select json_object_agg("unixdatetime",js)
from j