ok ci son riuscito
codice:
SELECT * 
FROM course_course_desc AS d,courses2categories AS l,course_course AS c LEFT OUTER JOIN (course_session AS s LEFT JOIN course_session_dates AS t ON s.id = t.course_session) ON s.course = c.id
WHERE (c.id = d.course) && (c.id = l.course) && (l.category = 1)
GROUP BY c.id ORDER BY c.id DESC