Q:

using SUM on foreign view's keys grouped on multiple key/values?

I had a question on executing SUM on rows from one table and inserting them in a column on another table where the calculated rows shared id with a row in the new table.
The solution worked very well for that instance. However, I have a similar situation in which that query no longer works.
I have this TABLE:
CREATE TABLE buildings (
    id SERIAL PRIMARY KEY UNIQUE,
    name character varying(20) NOT NULL UNIQUE,
    document jsonb
);

then this VIEW:
CREATE VIEW v_rooms AS  
SELECT buildings.id AS building_id,
    buildings.name AS building_name,
    jsonb_array_elements( document -> 'levels' ) -> 'meta' ->> 'level_number' AS level_number,
    ((jsonb_array_elements(jsonb_array_elements(buildings.document -> 'levels'::text) -> 'rooms'::text) -> 'meta'::text) ->> 'sqft'::text)::numeric AS sqft
FROM buildings
GROUP BY buildings.id;

finally in this VIEW:
CREATE OR REPLACE VIEW v_levels AS
SELECT
  buildings.id AS building_id,
  buildings.name AS building_name,
  jsonb_array_elements( document -> 'levels' ) -> 'meta' ->> 'level_number' AS number,
  sqft
FROM buildings

I want the COLUMN 'sqft' to be the SUM of all rows in v_rooms where v_rooms.building_id = v_levels.building_id AND v_rooms.level_number = v_levels.number.
I tried this VIEW definition:
CREATE OR REPLACE VIEW v_levels AS
SELECT
  buildings.id AS building_id,
  buildings.name AS building_name,
  jsonb_array_elements( document -> 'levels' ) -> 'meta' ->> 'level_number' AS number,
  sqft
FROM buildings
JOIN (
  SELECT building_id, level_number, sum(sqft) as sqft
  FROM v_rooms
  GROUP BY ( v_rooms.building_id, v_rooms.level_number )
) v_rooms ON ( v_rooms.building_id = buildings.id and v_rooms.level_number = level_number );

but I get duplicates, one row for the matching building_id and then again every time level number matches. which is an issue because level number is not unique to the table and only to the building.
FIDDLE

A:

You barely got it, once you have unnested the arrays you can simply aggregate the result by building.id, name and level in this way:
WITH ct AS
(
  SELECT 
    buildings.id AS building_id
    ,buildings.name AS building_name
    ,jsonb_array_elements( document -> 'levels' ) -> 'meta' ->> 'level_number' AS level_number
    ,((jsonb_array_elements(jsonb_array_elements(buildings.document->'levels')->'rooms')->'meta')->>'sqft')::numeric AS sqft
  FROM 
    buildings
)
SELECT
    building_id, building_name, level_number,
    SUM(sqft) AS sqft
FROM
    ct
GROUP BY
    building_id, building_name, level_number;

building_id | building_name | level_number | sqft
----------: | :------------ | :----------- | ---:
          1 | my blding     | 0            | 1300
          1 | my blding     | 1            | 1800

db<>fiddle here

