Kueri rekursif dengan jumlah di Postgres

Ini adalah versi sederhana dari benar @a_horse jawab (setelah berdiskusi dengan OP di komentar).
Bekerja dengan apa saja (cukup terbatas) jumlah level dalam rekursi.

Total harga untuk project_id yang diberikan

WITH RECURSIVE cte AS (
   SELECT project_id AS project_parent, project_value
   FROM   projects
   WHERE  project_id = 1 -- enter id of the base project here !

   UNION  ALL 
   SELECT p.project_id, p.project_value
   FROM   cte
   JOIN   projects p USING (project_parent)
)
SELECT sum(project_value) AS total_value
FROM   cte;

Total harga untuk semua proyek

WITH RECURSIVE cte AS (
   SELECT project_id, project_id AS project_parent, project_value
   FROM   projects
   WHERE  project_parent IS NULL  -- all base projects

   UNION  ALL 
   SELECT c.project_id, p.project_id, p.project_value
   FROM   cte c
   JOIN   projects p USING (project_parent)
   )
SELECT project_id, sum(project_value) AS total_value
FROM   cte
GROUP  BY 1
ORDER  BY 1;

db<>fiddle di sini (dengan test case yang benar)
_{Lama sqlfiddle}