我有一个包含任务的表的数据库。任务有一个生命周期。任务生命周期的状态可以改变。这些状态转换存储在单独的表 tasktransitions 中。现在我写了一个查询来查找所有打开/重新打开的任务和最近更改的任务,但我已经看到有相当少量的任务(<1000)执行时间变得非常长(>0.5s)。
任务
+-------------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+----------------+
| taskid | int(11) | NO | PRI | NULL | auto_increment |
| description | text | NO | | NULL | |
+-------------+---------+------+-----+---------+----------------+
任务转换
+------------------+-----------+------+-----+-------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------------+-----------+------+-----+-------------------+----------------+
| tasktransitionid | int(11) | NO | PRI | NULL | auto_increment |
| taskid | int(11) | NO | MUL | NULL | |
| status | int(11) | NO | MUL | NULL | |
| description | text | NO | | NULL | |
| userid | int(11) | NO | | NULL | |
| transitiondate | timestamp | NO | | CURRENT_TIMESTAMP | |
+------------------+-----------+------+-----+-------------------+----------------+
询问
SELECT tasks.taskid,tasks.description,tasklaststatus.status
FROM tasks
LEFT OUTER JOIN
(
SELECT tasktransitions.taskid,tasktransitions.transitiondate,tasktransitions.status
FROM tasktransitions
INNER JOIN
(
SELECT taskid,MAX(transitiondate) AS lasttransitiondate
FROM tasktransitions
GROUP BY taskid
) AS tasklasttransition ON tasklasttransition.lasttransitiondate=tasktransitions.transitiondate AND tasklasttransition.taskid=tasktransitions.taskid
) AS tasklaststatus ON tasklaststatus.taskid=tasks.taskid
WHERE tasklaststatus.status IS NULL OR tasklaststatus.status=0 or tasklaststatus.transitiondate>'2013-09-01';
上面查询的更易读、描述性更少的版本:
SELECT t.taskid, t.description,ls.status
FROM tasks AS t
LEFT OUTER JOIN
(
SELECT tt.taskid, tt.transitiondate, tt.status
FROM tasktransitions AS tt
INNER JOIN
(
SELECT taskid,MAX(transitiondate) AS transitiondate
FROM tasktransitions
GROUP BY taskid
) AS lt USING (taskid,transitiondate)
) AS ls USING (taskid)
WHERE ls.status IS NULL OR ls.status=0 or ls.transitiondate>'2013-09-01';
我想知道数据库结构是否是性能方面的最佳选择。添加索引有帮助吗?我已经尝试添加一些,但我没有看到很大的改进。
+-----------------+------------+----------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------------+------------+----------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| tasktransitions | 0 | PRIMARY | 1 | tasktransitionid | A | 896 | NULL | NULL | | BTREE | | |
| tasktransitions | 1 | taskid_date_ix | 1 | taskid | A | 896 | NULL | NULL | | BTREE | | |
| tasktransitions | 1 | taskid_date_ix | 2 | transitiondate | A | 896 | NULL | NULL | | BTREE | | |
| tasktransitions | 1 | status_ix | 1 | status | A | 3 | NULL | NULL | | BTREE | | |
+-----------------+------------+----------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
还有其他建议吗?