由于在 WHERE 子句中具有 notes 表的过滤器，因此 JOIN 的行为类似于 INNER JOIN ，将其移至 JOIN 条件:

Since you have the filter for the notes table in the WHERE clause the JOIN is acting like an INNER JOIN, move it to the JOIN condition:

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;

这也可以使用子查询来完成，因此您可以在子查询中应用注释过滤器:

This could also be done using a subquery, so you apply the notes filter inside the subquery:

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