我正在制作留言板,并试图检索常规主题(即未粘贴主题),并按最后发布的消息日期对其进行排序。但是,当我有大约10,000条消息和1500个主题时,我能够完成此任务,查询时间大于60秒。使用多连接和大记录集时的SQL查询优化
我的问题是,有什么我可以做我的查询来提高性能或是我的设计从根本上有缺陷?
这是我正在使用的查询。
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
编辑这里是解释计划
+----+--------------------+----------------+----------------+------------------+----------+---------+-------------------------+------+----------------------------------------------+
| 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 |
+----+--------------------+----------------+----------------+------------------+----------+---------+-------------------------+------+----------------------------------------------+
指标
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| 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 | |
+-------+------------+-----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
您至少应该发布解释计划。 – EvilTeach 2012-03-14 02:07:32
您使用的是什么RDBMS? – squillman 2012-03-14 02:09:47
没有查询计划=没有优化(尽管可能猜测应该存在的索引,哪些*也需要在问题中显示)。你有没有考虑用适当的'JOIN'替换'IN'? (我不使用MySQL,所以我不知道它是什么: - /) – 2012-03-14 02:14:39