Dit is een vereenvoudigde versie van @a_horse's correcte antwoord
(na discussie met OP in opmerkingen).
Werkt met elke (redelijk eindig) aantal niveaus in de recursie.
Totale prijs voor gegeven project_id
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;
Totale prijs voor alle projecten
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 hier
(met correcte testcase)
Oude sqlfiddle