How to optimise a complicated mysql query? - mysql

Question

When I EXPLIAN this:
EXPLIAN SELECT m.*,m.id AS mid FROM movie_category mc
LEFT JOIN movie m ON m.id=mc.movie_id
RIGHT JOIN movie_area ma ON ma.movie_id=mc.movie_id
LEFT JOIN area a ON a.id=ma.area_id
LEFT JOIN category c ON c.id=mc.category_id
WHERE 1 and ma.area_id>0
GROUP BY mid
ORDER BY m.read_count desc LIMIT 0,36;
I got this result:
+----+-------------+-------+------------+--------+-----------------+----------+---------+----------------------+-------+----------+---------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+--------+-----------------+----------+---------+----------------------+-------+----------+---------------------------------+
| 1 | SIMPLE | ma | NULL | ALL | NULL | NULL | NULL | NULL | 15545 | 100.00 | Using temporary; Using filesort |
| 1 | SIMPLE | mc | NULL | ref | movie_id | movie_id | 5 | flask.ma.movie_id | 2 | 100.00 | NULL |
| 1 | SIMPLE | m | NULL | eq_ref | PRIMARY,year_id | PRIMARY | 4 | flask.ma.movie_id | 1 | 100.00 | NULL |
| 1 | SIMPLE | a | NULL | eq_ref | PRIMARY | PRIMARY | 4 | flask.ma.area_id | 1 | 100.00 | Using index |
| 1 | SIMPLE | c | NULL | eq_ref | PRIMARY | PRIMARY | 4 | flask.mc.category_id | 1 | 100.00 | Using index |
+----+-------------+-------+------------+--------+-----------------+----------+---------+----------------------+-------+----------+---------------------------------+
5 rows in set, 1 warning (0.00 sec)
How to optimise this query? I really down't know what to do, help me out.
edit:
From the explain result,first line's Extra is "Using temporary; Using filesort",is not good.And second line's Extra and third line's Extra are all NULL, are also not good.
ps:
The query span 0.91 seconds,is very bad.How to add index to prove the query speed.

Answer 1

Improve schema
Without seeing the schemas involved, I will assume you have two many-to-many mapping table (mc, ma) that are inefficiently defined.
Follow the rules here ; you will gain some efficiency.
Get rid of unnecessary tables
category and movie_category are not really used in the query, so remove them from the query.
I assume this is a "generated" query? Then make the generation a little more sophisticated!