MySQL agregační funkce s LEFT JOIN

Protože máte filtr pro notes tabulky v WHERE klauzule JOIN se chová jako INNER JOIN , přesuňte jej do JOIN podmínka:

SELECT
  jobs.*,
  MAX(notes.`timestamp`) AS complete_date
FROM jobs
LEFT JOIN notes 
  ON (jobs.id=notes.job_id)
  AND (notes.type="complete" OR notes.type IS NULL)
WHERE (jobs.status="complete" OR jobs.status="closed")
GROUP BY jobs.id
ORDER BY complete_date ASC;

To lze také provést pomocí poddotazu, takže v poddotazu použijete filtr poznámek:

SELECT
  jobs.*,
  n.complete_date
FROM jobs
LEFT JOIN
(
    select job_id, MAX(`timestamp`) AS complete_date
    from notes 
    where (type="complete" OR type IS NULL)
    group by job_id
) n
  ON (jobs.id=n.job_id)
WHERE (jobs.status="complete" OR jobs.status="closed")
ORDER BY complete_date ASC