Question

下面描述了我想对这张表做些什么左边是一张表，我希望为每个事件计算'current_value' 代码1将current_value重置为值
代码2为current_value增加值 Code3使用值

减少current_value

Table Events                        |column to be calculated                                
eventId  deviceId EventCode value   |current_value                              
1          1        1          2    |2                          
2          1        2          1    |3                          
3          1        2          1    |4                          
4          1        2          1    |5                              
5          1        3          2    |3                              
6          1        2          2    |5                              
7          1        1          1    |1                              
8          1        2          2    |3          code 1: set                     
9          1        2          1    |4          code 2: add                     
10         1        2          1    |5          code 3: subtract                        
11         1        3          3    |2

我的SQL代码看起来像

Select                                                  
    EventId,                                                
    deviceId,                                               
    (select last(value) from Events as E where E.EventCode = 1 and E.DeviceID = DeviceID and E.EventId<EventId) AS LastSetValue,                                                
    (select last(value) from Events as E where E.EventCode = 1 and E.DeviceID = DeviceID and E.EventId<EventId) AS FromEventID,                                             
    (select sum(value) from Events as E where E.EventCode = 2 and E.DeviceID = DeviceID and E.EventId between fromEventId and EventId) AS SumOfAdded,                                               
    (select sum(value) from Events as E where E.EventCode = 3 and E.DeviceID = DeviceID and E.EventId betweein FromEventId and EventId) AS SumOfSubtracted,                                             
    LastSetValue+SumOfAdded-SumofSubtracted as current_value                                                
from Events;

此代码似乎不起作用因为子选择部分DeviceID看起来是内部临时表DeviceID，当我将外部DeviceID别名时，这也将无法工作，因为它无法找到。从EventID也有这个问题。

任何帮助，这里的错误将不胜感激。

Answer 1

我不确定我是否100％理解你的问题，但如果我正确地阅读了这些内容，你应该只需要对外表进行别名：

Select                                                  
    t.EventId,                                                
    t.DeviceId,                                               
    (select last(value) from Events as E where E.EventCode = 1 and E.DeviceID = t.DeviceID and E.EventId<t.EventId) AS LastSetValue,                                                
    (select last(value) from Events as E where E.EventCode = 1 and E.DeviceID = t.DeviceID and E.EventId<t.EventId) AS FromEventID,                                             
    (select sum(value) from Events as E where E.EventCode = 2 and E.DeviceID = t.DeviceID and E.EventId between fromEventId and t.EventId) AS SumOfAdded,                                               
    (select sum(value) from Events as E where E.EventCode = 3 and E.DeviceID = t.DeviceID and E.EventId between FromEventId and t.EventId) AS SumOfSubtracted,                                             
    LastSetValue+SumOfAdded-SumofSubtracted as current_value                                                
from Events t;

指的是subselect之外的别名

1 个答案: