存在查询时不会产生预期结果的T-SQL案例

Question

我已经汇总了一个查询，该查询应显示在选定日期之前和之后有事件的每条记录。添加了一个额外列，如果记录在日期之前有事件，则设置为True / False，如果记录在第二个日期之后有事件，则设置为相同。

问题是我知道事件表中有记录在第一个日期之前有事件，而不是在第二个日期之后但它们没有出现在我的查询中。只有两个结果为True的结果才会出现在查询中。不知道我做错了什么。

SELECT DISTINCT DeviceName,dPhone,DSIMID,  Vehicles.reg, DeviceID,
CASE
WHEN EXISTS (SELECT eventID FROM [events] WHERE [events].sysdatetime < 
'2018-09-05 11:46:00.000')
THEN 'True' ELSE 'False' 
END AS [WasReportingBeforeDate],
CASE
WHEN EXISTS (SELECT eventID FROM [events] WHERE [events].sysdatetime > 
'2018-09-05 11:46:00.000')
THEN 'True' ELSE 'False' END AS [WasReportingAfterDate]
FROM [Devices]
INNER JOIN Vehicles ON Vehicles.DevID = Devices.DevID
INNER JOIN [events] ON Devices.DevID = [events].DeviceID;

当前输出示例是：

Z3243   1  1 AA05 AAA 1 True    True

预期产出：

Z3243   1  1 AA05 AAA 1 True    False

此记录的数据比第二个日期更新，因此它应返回false

Answer 1

你没有关联你的EXISTS，所以如果[events].sysdatetime > '2018-09-05 11:46:00.000'表中存在任何记录，那么你的EXISTS将永远返回true。

你想要这样的东西：

...
CASE WHEN EXISTS (SELECT *
                  FROM [events] e2
                  WHERE e2.sysdatetime > '2018-09-05 11:46:00.000'
                  AND e2.eventID = e.eventID) --here
...
FROM [Devices] d
INNER JOIN Vehicles v ON b.DevID = d.DevID
INNER JOIN [events] e ON d.DevID = e.DeviceID;

Answer 2

我会将查询分解为2个单独的查询，并使用union all将结果集重新返回到一起。如果您需要一个标志来确定事件，然后才能将其硬编码到以下查询中。

   ;WITH EventsBefore AS 
    (
    SELECT DISTINCT
           DeviceName,
           dPhone,
           DSIMID,
           Vehicles.reg,
           DeviceID,
    FROM [Devices]
         INNER JOIN Vehicles ON Vehicles.DevID = Devices.DevID
         INNER JOIN [events] ON Devices.DevID = [events].DeviceID
         INNER JOIN lastEvent ON Devices.DevID = lastEvent.devID;
    WHERE [events].sysdatetime < '2018-09-05 11:46:00.000'

    )

     ,EventsAfter AS 
    (
    SELECT DISTINCT
           DeviceName,
           dPhone,
           DSIMID,
           Vehicles.reg,
           DeviceID,
    FROM [Devices]
         INNER JOIN Vehicles ON Vehicles.DevID = Devices.DevID
         INNER JOIN [events] ON Devices.DevID = [events].DeviceID
         INNER JOIN lastEvent ON Devices.DevID = lastEvent.devID;
    WHERE WHERE [events].sysdatetime > '2018-09-05 11:46:00.000'

    )

    SELECT * FROM EventsBefore
    UNION ALL 
    SELECT * FROM EventsAfter

Answer 3

1. 摆脱加入events并随意删除多余的DISTINCT
2. 将连接谓词放入现在缺少它的子查询中

像那样：

SELECT DeviceName,dPhone,DSIMID,  Vehicles.reg, DeviceID,
CASE
  WHEN EXISTS (SELECT 1 FROM [events] e 
    WHERE e.sysdatetime < '2018-09-05 11:46:00.000'
    AND e.DeviceID = Devices.DevID)
  THEN 'True' ELSE 'False' 
END AS [WasReportingBeforeDate],
CASE
  WHEN EXISTS (SELECT 1 FROM [events] e 
    WHERE e.sysdatetime > '2018-09-05 11:46:00.000'
    AND e.DeviceID = Devices.DevID)
THEN 'True' ELSE 'False' END AS [WasReportingAfterDate]
FROM [Devices]
INNER JOIN Vehicles ON Vehicles.DevID = Devices.DevID