I am making a message board and I trying to retrieve regular topics (ie, topics that are not stickied) and sort them by the date of the last posted message. I am able to accomplish this however when I have about 10,000 messages and 1500 topics the query time is >60 seconds.
My question is, is there anything I can do to my query to increase performance or is my design fundamentally flawed?
Here is the query that I am using.
SELECT Messages.topic_id,
Messages.posted,
Topics.title,
Topics.user_id,
Users.username
FROM Messages
LEFT JOIN
Topics USING(topic_id)
LEFT JOIN
Users on Users.user_id = Topics.user_id
WHERE Messages.message_id IN (
SELECT MAX(message_id)
FROM Messages
GROUP BY topic_id)
AND Messages.topic_id
NOT IN (
SELECT topic_id
FROM StickiedTopics)
AND Messages.posted IN (
SELECT MIN(posted)
FROM Messages
GROUP BY message_id)
AND Topics.board_id=1
ORDER BY Messages.posted DESC LIMIT 50
Edit Here is the Explain Plan
+----+--------------------+----------------+----------------+------------------+----------+---------+-------------------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+----------------+----------------+------------------+----------+---------+-------------------------+------+----------------------------------------------+
| 1 | PRIMARY | Topics | ref | PRIMARY,board_id | board_id | 4 | const | 641 | Using where; Using temporary; Using filesort |
| 1 | PRIMARY | Users | eq_ref | PRIMARY | PRIMARY | 4 | spergs3.Topics.user_id | 1 | |
| 1 | PRIMARY | Messages | ref | topic_id | topic_id | 4 | spergs3.Topics.topic_id | 3 | Using where |
| 4 | DEPENDENT SUBQUERY | Messages | index | NULL | PRIMARY | 8 | NULL | 1 | |
| 3 | DEPENDENT SUBQUERY | StickiedTopics | index_subquery | topic_id | topic_id | 4 | func | 1 | Using index |
| 2 | DEPENDENT SUBQUERY | Messages | index | NULL | topic_id | 4 | NULL | 3 | Using index |
+----+--------------------+----------------+----------------+------------------+----------+---------+-------------------------+------+----------------------------------------------+
Indexes
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Messages | 0 | PRIMARY | 1 | message_id | A | 9956 | NULL | NULL | | BTREE | |
| Messages | 0 | PRIMARY | 2 | revision_no | A | 9956 | NULL | NULL | | BTREE | |
| Messages | 1 | user_id | 1 | user_id | A | 432 | NULL | NULL | | BTREE | |
| Messages | 1 | topic_id | 1 | topic_id | A | 3318 | NULL | NULL | | BTREE | |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Topics | 0 | PRIMARY | 1 | topic_id | A | 1205 | NULL | NULL | | BTREE | |
| Topics | 1 | user_id | 1 | user_id | A | 133 | NULL | NULL | | BTREE | |
| Topics | 1 | board_id | 1 | board_id | A | 1 | NULL | NULL | | BTREE | |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
+-------+------------+-----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+-----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Users | 0 | PRIMARY | 1 | user_id | A | 2051 | NULL | NULL | | BTREE | |
| Users | 0 | username_UNIQUE | 1 | username | A | 2051 | NULL | NULL | | BTREE | |
+-------+------------+-----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
I would start with the first basis of qualified topics, get those IDs, then join out after. My inner first query does a pre-qualify grouped by topic_id and max message to just get distinct IDs pre-qualified. I've also applied a LEFT JOIN to the stickiesTopics too. Why? By doing a left-join, I can look for those that are FOUND (those you want to exclude). So I've applied a WHERE clause for Stickies topic ID is NULL (ie: NOT found). So by doing this, we've ALREADY paired down the list SIGNIFICANTLY without doing several nested sub-queries. From THAT result, we can join to the messages, topics (including qualifier of board_id = 1), users and get parts as needed. Finally, apply a single WHERE IN sub-select for your MIN(posted) qualifier. Don't understand the basis of that, but left it in as part of your original query. Then the order by and limit.
SELECT STRAIGHT_JOIN
M.topic_id,
M.posted,
T.title,
T.user_id,
U.username
FROM
( select
M1.Topic_ID,
MAX( M1.Message_id ) MaxMsgPerTopic
from
Messages M1
LEFT Join StickiedTopics ST
ON M1.Topic_ID = ST.Topic_ID
where
ST.Topic_ID IS NULL
group by
M1.Topic_ID ) PreQuery
JOIN Messages M
ON PreQuery.MaxMsgPerTopic = M.Message_ID
JOIN Topics T
ON M.Topic_ID = T.Topic_ID
AND T.Board_ID = 1
LEFT JOIN Users U
on T.User_ID = U.user_id
WHERE
M.posted IN ( SELECT MIN(posted)
FROM Messages
GROUP BY message_id)
ORDER BY
M.posted DESC
LIMIT 50