Question

我需要一些帮助来编写查询，以显示未向我们报告录音的测量设备列表以及自上次录制以来的天数。

这是表结构：

select d.deviceno, r.lastrecordingdate, --Here's where i need a table to act as a COUNT for --number of days the device has not logged.
from modules m
join devices d on m.deviceid = d.deviceid
join recordings r on m.recordingid = r.recordingid
--i really don't know what to write beyond this. I am drawin

Answer 1

SELECT D.deviceno, 
       DateDiff(day, CURRENT_TIMESTAMP, max_date) AS days_since
  FROM (
          SELECT D.deviceno,
                 COALESCE(MAX(R.last_recordingdate), '2000-01-01') AS max_date
            FROM Modules M
                 INNER JOIN Devices D
                    ON M.deviceid = D.deviceid
                 LEFT JOIN Recordings R 
                    ON M.recordingid = R.recordingid
                 GROUP BY D.deviceno
        ) FOO
  WHERE max_date < DateAdd(day, -7, CURRENT_TIMESTAMP)

由于您没有指定数据库，我使用的是SQL Server特定语法（日期数学函数）。 COALESCE旨在确保我们捕获未记录任何内容的设备。

用于列出没有当前日期戳的项的SQL查询

1 个答案: