当多个规则处于活动状态时如何计算子查询的总和？

Question

我正在尝试使用以下规则根据以下 session_values table 计算 val 字段的总和：

事件字段只能有 'start' 和 'stop' 值
当sessionid同时具有两种事件类型时，将使用'stop'事件的val字段进行计算。例如，10 将用于 sessionid 1，5 将用于 session id 4

如果sessionid只有'start'或者'stop'，sessionid会使用val字段。比如sessionid 2的值为6，sessionid的值为5 将是 7

mysql> select * from session_values;
+-------------------------+-----------+-------+------+
| time                    | sessionid | event | val  |
+-------------------------+-----------+-------+------+
| 2019-07-24 15:52:24.671 | 1         | start |    5 |
| 2019-07-24 15:52:27.730 | 1         | stop  |   10 |
| 2019-07-24 15:52:30.658 | 2         | stop  |    6 |
| 2019-07-24 15:52:33.919 | 3         | stop  |    8 |
| 2019-07-24 15:52:44.671 | 4         | start |    5 |
| 2019-07-24 15:52:47.293 | 4         | stop  |    5 |
| 2019-07-24 16:36:03.097 | 5         | start |    7 |
| 2019-07-24 16:36:09.399 | 6         | start |    3 |
+-------------------------+-----------+-------+------+

详情请参考以下url： http://www.sqlfiddle.com/#!9/23b7a1/4

我使用以下 sql 代码来计算只有一个事件的 sessionid 的总和：

select sum(val) from ( 
  select * from (select * from session_values ) s1 
  where s1.event in ('start','stop') 
  group by sessionid  
  HAVING COUNT(DISTINCT s1.event) = 1
) s2 ;

按预期工作并且 returned 24

对于具有多个事件的 sessionid，以下 sql：

select sum(val) from ( 
  select * from (select * from session_values ) s1 
  where s1.event in ('start','stop') 
  group by sessionid  
  HAVING COUNT(DISTINCT s1.event) = 2
) s2 ;

我有两个问题：

第一个问题是，我无法找到一种方法来确保只有 'stop' 个事件将 returned 用于第二个 SQL（具有多个事件）意思当运行以下查询时，我只得到 'start' 事件。是否可以将查询增强为仅 return 'stop' 个事件？

select * from ( 
  select * from (select * from session_values ) s1 
  where s1.event in ('start','stop') 
  group by sessionid  
  HAVING COUNT(DISTINCT s1.event) = 2
) s2 ;
+-------------------------+-----------+-------+------+
| time                    | sessionid | event | val  |
+-------------------------+-----------+-------+------+
| 2019-07-24 15:52:24.671 | 1         | start |    5 |
| 2019-07-24 15:52:44.671 | 4         | start |    5 |
+-------------------------+-----------+-------+------+

第二个问题是，我想结合一个 SQL 查询来根据解释的规则计算值的总和。是否可以将两者结合起来 SQL ?

Answer 1

stop 个启停对事件

select *
from session_values
where sessionid in (
                    select sessionId 
                    from session_values
                    where event in ('start','stop')
                    group by sessionid  
                    HAVING COUNT(1)=2
                  )
    and event='stop'

总和：

select sum(val)
from session_values
where sessionid in (
                    select sessionId 
                    from session_values
                    where event in ('start','stop')
                    group by sessionid  
                    HAVING COUNT(1)=2
                  )
    and event='stop'
 or sessionid in (
                    select sessionId 
                    from session_values
                    where event in ('start','stop')
                    group by sessionid  
                    HAVING COUNT(1)=1
                  )
    and event='start'

当多个规则处于活动状态时如何计算子查询的总和？

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