如何获得具有上限的 MAX()？

Question

我正在使用下面的查询来生成报告。我需要生成报告，因此它仅适用于最大时间戳（例如直到昨天，2016-08-02）。为此，我需要修改查询的第二行，以便我不再获得eventsink.blueboxevent.created大于昨天限制的值。

例如，如果我在下面的示例数据上运行报告，要求只查看截至昨天 (2016-08-02) 的时间范围，我希望看到如下记录：

想要的结果

device1 | 2016-08-02

样本数据

DeviceID | eventsink.blueboxevent.created
device1 | 2016-08-03
device1 | 2016-08-02
device1 | 2016-08-01

要修改的当前查询

SELECT eventsink.blueboxevent.deviceid     AS 'Device ID', 
       Max(eventsink.blueboxevent.created) AS 'Last Connection', 
       provisioned, 
       Max(softwareversion)                AS 'S/W Ver.', 
       buildingname                        AS 'Name', 
       buildingaddr1                       AS 'Address', 
       buildingcity                        AS 'City', 
       buildingstate                       AS 'State', 
       zipcode                             AS 'Zip Code', 
       countrycode                         AS 'Cnty' 
FROM   eventsink.blueboxevent 
       JOIN md.elevator 
         ON md.elevator.deviceid = eventsink.blueboxevent.deviceid 
       JOIN eventsink.blueboxmasterdataevent 
         ON eventsink.blueboxmasterdataevent.deviceid = 
            eventsink.blueboxevent.deviceid 
       JOIN (SELECT Min(eventenqueuedutctime) AS 'Provisioned', 
                    deviceid 
             FROM   eventsink.blueboxevent 
             WHERE  id = '1' 
             GROUP  BY deviceid) t 
         ON eventsink.blueboxevent.deviceid = t.deviceid 
WHERE  ( id = '9' 
         AND softwareversion LIKE '[1-2][.]%' ) 
GROUP  BY eventsink.blueboxevent.deviceid, 
          provisioned, 
          buildingname, 
          buildingaddr1, 
          buildingcity, 
          buildingstate, 
          zipcode, 
          countrycode 
ORDER  BY provisioned DESC 

Answer 1

改变：

MAX(created)

用一个CASE表达式：

MAX(CASE WHEN created <= '2015-12-31' THEN created ELSE NULL END)

在ELSE NULL不需要，因为它是默认的。现在，如果您想返回，'2015-12-31以防在阈值日期之前没有日期，我们可以使用ISNULL()或COALESCE：

COALESCE( MAX(CASE WHEN created <= '2015-12-31' THEN created END), '2015-12-31' )

或者，如果在这种情况下，您想要下一个可用日期，即使它大于阈值日期：

COALESCE( MAX(CASE WHEN created <= '2015-12-31' THEN created END), MIN(created) )

注意：答案假定created是 a DATE（或DATETIME没有时间部分的 a）。如果它确实有时间部分，我建议你替换使用<=with <（即替换<= '2015-12-31'with < '2016-01-01'）。在 Aaron Bertrand 的博客文章中查看对包含边界问题的详细解释：What do and the evil have inclusive ？BETWEEN