mysql short union - sql

Question

I'm far from being a mysql guru, so need to know if there's a way to make this query faster,shorter and more compact.
(SELECT DISTINCT(cfrm.nid), f.filename, n.title, n.created
FROM content_field_raamatu_marksonad cfrm
LEFT JOIN node n ON (n.nid = cfrm.nid)
LEFT JOIN content_field_kaanepilt cfk ON (cfk.nid = n.nid)
LEFT JOIN files f ON (f.fid = cfk.field_kaanepilt_fid)
WHERE n.type = 'raamat'
AND n.status = 1
AND cfrm.field_raamatu_marksonad_value IN (102, 3348))
UNION
(SELECT DISTINCT(cfrt.nid), f.filename, n.title, n.created
FROM content_field_raamatu_teema cfrt
LEFT JOIN node n ON (n.nid = cfrt.nid)
LEFT JOIN content_field_kaanepilt cfk ON (cfk.nid = n.nid)
LEFT JOIN files f ON (f.fid = cfk.field_kaanepilt_fid)
WHERE n.type = 'raamat'
AND n.status = 1
AND cfrt.field_raamatu_teema_value = 1342)
ORDER BY `created` DESC

Answer 1

About the only way to rewrite it is to do the UNION before you do the LEFT JOINs:
SELECT DISTINCT x.nid, f.filename, n.title, n.created
FROM (SELECT DISTINCT cfrm.nid
FROM content_field_raamatu_marksonad AS cfrm
WHERE cfrm.field_raamatu_marksonad_value IN (102, 3348)
UNION
SELECT DISTINCT cfrt.nid
FROM content_field_raamatu_teema AS cfrt
WHERE cfrt.field_raamatu_teema_value = 1342) AS x
LEFT JOIN node AS n ON n.nid = x.nid
LEFT JOIN content_field_kaanepilt AS cfk ON cfk.nid = n.nid
LEFT JOIN files AS f ON f.fid = cfk.field_kaanepilt_fid
WHERE n.type = 'raamat'
AND n.status = 1
ORDER BY n.created DESC;
This might save dual scans of the outer joined tables. On the other hand, the optimizer might optimize it like that anyway - though I suspect it probably would not. Replacing the LEFT JOIN operations with JOIN would improve performance - if it does not affect the accuracy of the result. That depends on whether you expect there to be a file name for every row or not - at least in part.