left join

SELECT c.lvl,
       sum(c.q) AS q,
       sum(coalesce(c.q * fe.value,0))/sum(c.q) AS fe,
       sum(coalesce(c.q * zn.value,0))/sum(c.q) AS zn,
       sum(coalesce(c.q * s.value,0))/sum(c.q) AS s
FROM
  (SELECT d.value AS q,
                     c.id,
                     EXTRACT (hour
                              FROM d.f_timestamp), lvl.value AS lvl,
                     d.f_timestamp AS time,
                     t.name_id
   FROM
     (SELECT *
      FROM vgok_site.a_analiz_data
      WHERE elem_id = 6) d,

     (SELECT *
      FROM vgok_site.a_analiz_data
      WHERE elem_id = 84) lvl,
        vgok_site.a_analiz_create c,
        vgok_site.a_template t
   WHERE d.analiz_id = c.id
     AND lvl.analiz_id = c.id
     AND c.template_id = t.id
     AND t.id = 77
     AND d.value IS NOT NULL
     AND '2016-05-05' = to_char(c.f_timestamp, 'YYYY-MM-DD')) c
LEFT JOIN
  (SELECT *
   FROM vgok_site.a_analiz_data fe
   WHERE fe.elem_id = 33) fe ON fe.analiz_id = c.id
LEFT JOIN
  (SELECT *
   FROM vgok_site.a_analiz_data zn
   WHERE zn.elem_id = 2) zn ON zn.analiz_id = c.id
LEFT JOIN
  (SELECT *
   FROM vgok_site.a_analiz_data s
   WHERE s.elem_id = 8) s ON s.analiz_id = c.id
GROUP BY c.lvl