This query runs pretty slow on my ThinkUp installation, over a second. Can we optimize it to use indexes and run faster? Here's my output:

```

mysql> EXPLAIN SELECT i.network_user_id, i.network_username, i.crawler_last_run, i.total_posts_by_owner, i.total_posts_in_system, i.posts_per_day, i.posts_per_week, i.percentage_replies, i.percentage_links, i.network, count(p.author_user_id) AS period_number_posts FROM tu_posts p RIGHT JOIN (SELECT * FROM tu_instances WHERE network= 'twitter' ) AS i ON p.author_user_id = i.network_user_id AND CONVERT_TZ(p.pub_date,'+00:00','+02:00') >= '2013-09-29 00:00:00' AND CONVERT_TZ(p.pub_date,'+00:00','+02:00') <= '2013-09-29 23:59:59' GROUP BY i.network_user_id ORDER BY period_number_posts DESC ;
+----+-------------+--------------+------+----------------+----------------+---------+-------------------+------+---------------------------------+
| id | select_type | table        | type | possible_keys  | key            | key_len | ref               | rows | Extra                           |
+----+-------------+--------------+------+----------------+----------------+---------+-------------------+------+---------------------------------+
|  1 | PRIMARY     | <derived2>   | ALL  | NULL           | NULL           | NULL    | NULL              |    2 | Using temporary; Using filesort |
|  1 | PRIMARY     | p            | ref  | author_user_id | author_user_id | 92      | i.network_user_id |    7 |                                 |
|  2 | DERIVED     | tu_instances | ALL  | NULL           | NULL           | NULL    | NULL              |    5 | Using where                     |
+----+-------------+--------------+------+----------------+----------------+---------+-------------------+------+---------------------------------+
3 rows in set (0.03 sec)

mysql> SELECT i.network_user_id, i.network_username, i.crawler_last_run, i.total_posts_by_owner, i.total_posts_in_system, i.posts_per_day, i.posts_per_week, i.percentage_replies, i.percentage_links, i.network, count(p.author_user_id) AS period_number_posts FROM tu_posts p RIGHT JOIN (SELECT * FROM tu_instances WHERE network= 'twitter' ) AS i ON p.author_user_id = i.network_user_id AND CONVERT_TZ(p.pub_date,'+00:00','+02:00') >= '2013-09-29 00:00:00' AND CONVERT_TZ(p.pub_date,'+00:00','+02:00') <= '2013-09-29 23:59:59' GROUP BY i.network_user_id ORDER BY period_number_posts DESC ;
+-----------------+------------------+---------------------+----------------------+-----------------------+---------------+----------------+--------------------+------------------+---------+---------------------+
| network_user_id | network_username | crawler_last_run    | total_posts_by_owner | total_posts_in_system | posts_per_day | posts_per_week | percentage_replies | percentage_links | network | period_number_posts |
+-----------------+------------------+---------------------+----------------------+-----------------------+---------------+----------------+--------------------+------------------+---------+---------------------+
| 930061          | ginatrapani      | 2013-12-14 18:49:24 |                 8710 |                  8710 |          1.57 |          10.97 |              42.93 |            20.47 | twitter |                   0 |
| 100127476       | thinkup          | 2013-08-06 13:49:17 |                 1014 |                  1015 |          0.37 |           2.58 |              47.09 |            43.65 | twitter |                   0 |
+-----------------+------------------+---------------------+----------------------+-----------------------+---------------+----------------+--------------------+------------------+---------+---------------------+
2 rows in set (1.12 sec)


```