Question

我目前正在尝试优化MySQL语句。它需要大约10秒并输出两个整数的平均差。事件表包含6个cols，并由它的id和run_id +每个其他键索引。

该表包含run_id 37的3308000行，总共4162050行。加入似乎需要大部分时间，所以也许有办法加快加速。

send.element_id和recv.element_id是唯一的，有没有办法在sql中表达它可能会带来更好的性能？

|-------------------
|Spalte      Typ 
|-------------------
|run_id      int(11)
|element_id  int(11)
|event_id    int(11)      PRIMARY
|event_time  int(11)
|event_type  varchar(20)
|event_data  varchar(20)

查询：

select avg(recv.event_time-send.event_time)
from 
(
 select element_id, event_time
 from event
 where run_id = 37 and event_type='SEND_FLIT'
) send,
(
 select element_id, event_time
 from event
 where run_id = 37 and event_type='RECV_FLIT'
) recv
where recv.element_id = send.element_id

查询说明：

+----+-------------+------------+------+-----------------------------------------------------+-------------+---------+-------------+--------+-----------------------+
| id | select_type | table      | type | possible_keys                                       | key         | key_len | ref         | rows   | extra                 |
+----+-------------+------------+------+-----------------------------------------------------+-------------+---------+-------------+--------+-----------------------+
|  1 | PRIMARY     | <derived3> | ALL  | NULL                                                | NULL        | NULL    | NULL        | 499458 | NULL                  |
|  1 | PRIMARY     | <derived2> | ref  | <auto_key0>                                         | <auto_key0> | 4       | element_id  | 10     | NULL                  |
|  3 | DERIVED     | event      | ref  | run_id,run_id_2,run_id_3,run_id_4,run_id_5,run_id_6 | run_id_5    | 26      | const,const | 499458 | Using index condition |
|  2 | DERIVED     | event      | ref  | run_id,run_id_2,run_id_3,run_id_4,run_id_5,run_id_6 | run_id_5    | 26      | const,const | 562556 | Using index condition |
+----+-------------+------------+------+-----------------------------------------------------+-------------+---------+-------------+--------+-----------------------+

Answer 1

一种方法是按element_id进行分组，然后使用sum确定差异，然后将其传递给avg。

select avg(diff) from (
    select 
        sum(case when event_type = 'SEND_FLIT' then -1 * event_time else event_time end)
        as diff
    from event
    where run_id = 37
    and event_type in ('SEND_FLIT','RECV_FLIT')
    group by element_id
) t

MySQL：优化加入

1 个答案: