查找表中缺少的时间间隔 [英] Find missing time intervals in a table

问题描述

我有下表，其中包含每15分钟从几个不同设备读取的值:

I have the following table which contains values read every 15 minutes from several different devices:

ID   DeviceID   Date                    Value
----------------------------------------------
1    3          24.08.2011 00:00:00     0.51
2    3          24.08.2011 00:15:00     2.9
3    3          24.08.2011 00:30:00     0
4    3          24.08.2011 00:45:00     7.1
5    3          24.08.2011 01:00:00     1.05
6    3          24.08.2011 03:15:00     3.8

我想在表中找到给定月份内没有条目的每台设备的所有差距.对于上表，结果应该是这样的:

I'd like to find all the gaps in the table for each device, where there are no entries, for a given month. For the table above, the result should be something like this:

DeviceID    StartDate               EndDate
-------------------------------------------------------
3           24.08.2011 01:00:00     24.08.2011 03:15:00

该表大约有35000台设备和1亿个条目.

The table has roughly 35000 devices and 100 million entries.

这是我尝试过的；它很慢，但是返回我需要的.但是，除了速度之外，还有另一个问题:它只能找到在给定月份设备的最后一个条目之前丢失的时间间隔；之后的所有内容都将被忽略，因此有可能会错过额外的缺失值间隔.

This is what I tried; it's rather slow, but returns what I need. However, besides its speed, there's another problem: it only finds missing intervals up to the last entry for a device in the given month; anything after that will be ignored, so it's possible to miss an extra interval of missing values.

SELECT
    t2.Date AS StartDate
    , t1.Date AS EndDate
FROM
    TestTable t1
    INNER JOIN TestTable t2 ON t1.DeviceID = t2.DeviceID
WHERE
    (t2.Date = (SELECT MAX(Date) FROM TestTable t3 WHERE t3.Date < t1.Date AND t3.DeviceID = t1.DeviceID)
        AND DATEDIFF(MINUTE, t2.Date, t1.Date) > 15)
    AND t1.DeviceID = @id
    AND DATEPART(YEAR, t1.Date) = @year AND DATEPART(MONTH, t1.Date) = @month

推荐答案

以下操作应该有效，并且不会仅返回一个deviceid的单个记录.

Following should work and doesn't return just a single record for a deviceid.

要点是

• 为每个记录添加一个行号，按Date的顺序排列，并为每个DeviceID重新启动.
• 与self一起创建包含两个原始行的组合的行的结果.每行的列之间的关系是行号(+1)和DeviceID.
• 仅保留相关Date超过15分钟的行.

• Add a rownumber to each record, ordered by Date and restarting for each DeviceID.
• Join with self to create a result with rows consisting of the combination of two original rows. The relation between the columns of each row is the rownumber (+1) and the DeviceID.
• Only retain those rows where the related Date is more than 15 minutes.

SQL语句

;WITH t AS (
  SELECT  *, rn = ROW_NUMBER() OVER (PARTITION BY DeviceID ORDER BY Date)
  FROM    TestTable
)  
SELECT  t1.DeviceID, t1.Date, t2.Date
FROM    t t1
        INNER JOIN t t2 ON t2.DeviceID = t1.DeviceID AND t2.rn = t1.rn + 1
WHERE   DATEDIFF(MINUTE, t1.Date, t2.Date) > 15        

测试脚本

;WITH TestTable (ID, DeviceID, Date, Value) AS (
  SELECT 1, 3, '2011-08-24 00:00:00', 0.51 UNION ALL
  SELECT 2, 3, '2011-08-24 00:15:00', 2.9 UNION ALL
  SELECT 3, 3, '2011-08-24 00:30:00', 0 UNION ALL
  SELECT 4, 3, '2011-08-24 00:45:00', 7.1 UNION ALL
  SELECT 5, 3, '2011-08-24 01:00:00', 1.05 UNION ALL
  SELECT 6, 3, '2011-08-24 03:15:00', 3.8 
)
, t AS (
  SELECT  *, rn = ROW_NUMBER() OVER (PARTITION BY DeviceID ORDER BY Date)
  FROM    TestTable
)  
SELECT  t1.DeviceID, t1.Date, t2.Date
FROM    t t1
        INNER JOIN t t2 ON t2.DeviceID = t1.DeviceID AND t2.rn = t1.rn + 1
WHERE   DATEDIFF(MINUTE, t1.Date, t2.Date) > 15        

这篇关于查找表中缺少的时间间隔的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！