在子查询 where 子句中引用列

Question

我有一个 table 有多个会话事件的记录。每一行都是一个会话中的一个事件，一个会话可以有多个相同的事件。这些基本上是游戏环节，每个事件都是回合开始或回合结束。我的数据看起来像

Session_id | Event_type | Event_Time
1 | round_start | 12:01:00
1 | round_end | 12:02:00
1 | round_start| 12:05:00
1 | round_end | 12:7:00
2 | round_start | 14:11:00
2 | round_end | 14:12:00
3 | round_start| 15:09:00
3 | round_end | 15:13:00

我正在尝试查找平均回合持续时间。我尝试了以下 SQL

select
RS.session_id,
RS.Event_Time as StartTime,
RE.EndTime,
TIMESTAMPDIFF(MINUTE,RE.EndTime,RS.Event_Time) as duration
from amp_event_mamlaka as RS
left join 
(
    select session_id, min(event_time) as EndTimd from amp_event_mamlaka 
    where Event_Type = "Round End" and session_id = RS.session_id and  event_time>RS.Event_Time
) RE
on RE.session_id = RS.session_id

问题是我无法在加入的 table 中引用 RS.session_id 和 RS.event_time。

我正在使用 MySQL。关于如何实现这一点有什么建议吗？

谢谢

Answer 1

与其将其保留在 subquery 的 where 子句中，不如将条件保留在 Join On 子句中。试试这个。

SELECT RS.session_id,
       RS.Event_Time                                    AS StartTime,
       RE.EndTime,
       Timestampdiff(MINUTE, RE.EndTime, RS.Event_Time) AS duration
FROM   amp_event_mamlaka AS RS
       LEFT JOIN (SELECT session_id,
                         Min(event_time) AS EndTimd
                  FROM   amp_event_mamlaka
                  WHERE  Event_Type = "Round End") RE
              ON RE.session_id = RS.session_id
                 AND RE.event_time > RS.Event_Time

Answer 2

我建议您使用相关子查询来解决这个问题：

select RS.session_id, RS.Event_Time as StartTime,
       (select smin(event_time) 
        from amp_event_mamlaka em
        where em.session_id = RS.session_id and
              em.Event_Type = 'Round End' and 
              em.event_time > RS.Event_Time
       ) as EndTime,
from amp_event_mamlaka RS;

您可以使用子查询进行时间戳差异：

select RS.*, TIMESTAMPDIFF(MINUTE, EndTime, Event_Time) as duration
from (select RS.session_id, RS.Event_Time as StartTime,
             (select min(event_time) 
              from amp_event_mamlaka em
              where em.session_id = RS.session_id and
                    em.Event_Type = 'Round End' and 
                    em.event_time > RS.Event_Time
             ) as EndTime
      from amp_event_mamlaka RS
     ) RS

Answer 3

与嵌套查询相反，子查询应该只有 return 一个值。您的要求是一个示例，您需要来自成对行的数据。子查询仅用于连接对，不提供数据。 Fiddle

select  e1.SessionID, e1.EventType, e1.EventTime, e2.EventType, e2.EventTime, TimeStampDiff( minute, e1.EventTime, e2.EventTime ) Duration
from    Events  e1
join    Events e2
    on  e2.SessionID    = e1.SessionID
    and e2.EventType    = 'end'
    and e2.EventTime    =(
        select  Min( EventTime )
        from    Events
        where   SessionID   = e1.SessionID
            and EventType   = 'end'
            and EventTime   > e1.EventTime )
where   e1.EventType = 'start';

在子查询 where 子句中引用列

Referencing a column in a sub-query's where clause

mysql

sql

left-join

where-clause