mysql join 2 tabeller - vis alle rækker fra en tabel

Du bør være i stand til at bruge en LEFT JOIN for at opnå dette.

SELECT a.id AS stock, COALESCE(b.quanitity,0), b.product_id, a.name AS stock_fullname
FROM a
LEFT JOIN b
  ON a.id = b.stock_id
  AND b.product_id = 13