[英]Improving MySQL query performance when using SUM
我有一个用户生成的内容表,其中包括用于状态的ENUM格式列。 (待定,已批准,自动批准或已拒绝)为了按状态关注最近内容的数量,我使用以下查询:
mysql> SELECT DATE(dt_submitted) AS date,
COUNT(*) AS count,
SUM(IF(status='Approved', 1, 0)) as approved,
SUM(IF(status='Approved-auto', 1, 0)) as approved_auto,
SUM(IF(status='Rejected', 1, 0)) as rejected,
SUM(IF(status='Pending', 1, 0)) as pending
FROM post
WHERE dt_submitted > DATE_SUB(CURDATE(), INTERVAL 30 DAY)
GROUP BY date;
+------------+-------+----------+---------------+----------+---------+
| date | count | approved | approved_auto | rejected | pending |
+------------+-------+----------+---------------+----------+---------+
| 2011-11-22 | 131 | 124 | 0 | 7 | 0 |
| 2011-11-23 | 116 | 114 | 0 | 2 | 0 |
...
| 2011-12-21 | 690 | 674 | 5 | 11 | 0 |
| 2011-12-22 | 80 | 75 | 0 | 4 | 38 |
+------------+-------+----------+---------------+----------+---------+
31 rows in set (0.60 sec)
这几乎是完美的,但是我很挑剔,想看看我是否可以使其更快。 (在此服务器上,0.6秒的速度很慢,并且该表经常更改,以免担心将静态日期传递给缓存结果。)
如果我解释该查询,则它不使用任何索引( status
已建立索引)。 (这是因为它是指为SUM创建的临时表吗?)
explain SELECT DATE(dt_submitted) AS date, COUNT(*) AS count, SUM(IF(status='Approved', 1, 0)) as approved, SUM(IF(status='Approved-auto', 1, 0)) as approved_auto, SUM(IF(status='Rejected', 1, 0)) as rejected, SUM(IF(status='Pending', 1, 0)) as pending FROM post WHERE dt_submitted > DATE_SUB(CURDATE(), INTERVAL 30 DAY) GROUP BY date;
+----+-------------+-------+------+---------------+------+---------+------+--------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+--------+----------------------------------------------+
| 1 | SIMPLE | post | ALL | NULL | NULL | NULL | NULL | 529902 | Using where; Using temporary; Using filesort |
+----+-------------+-------+------+---------------+------+---------+------+--------+----------------------------------------------+
1 row in set (0.00 sec)
那么,有什么我可以做的来优化表或重写查询以使其更快? 还是此查询只是受可用系统资源速度的限制?
编辑: dt_submitted
没有索引。
仔细检查是否已索引适当的列。
(如编辑中所述,我无法仔细检查索引。对适当的列建立索引后,问题已解决。)
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