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POSQL Query to aggregate DateDiff greater than given value
 

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    <p>I have a logging table used for device “heartbeats”. I have these network devices that check-in/heartbeat with the server every 10 minutes. We are wanting statistics on when they miss their scheduled check-in time. I have a query that can do this on a per-device basis, but I need it to be modified to handle across all devices.</p> <p>The heartbeat table looks like this:</p> <pre><code>CREATE TABLE [dbo].[DeviceHeartbeat]( [Id] [int] IDENTITY(1,1) NOT NULL, [DeviceId] [int] NULL, [CheckinTime] [datetime] NULL, [Runtime] [int] NULL, PRIMARY KEY CLUSTERED ([Id] ASC)) ON [PRIMARY] </code></pre> <p>Device checks into the server, the server adds a row to this table with its Id, the CheckinTime and the device’s runtime (a hardware value sent by the device). The query I have currently looks like this:</p> <pre><code>WITH t AS ( SELECT Checkintime, rn = ROW_NUMBER() OVER (ORDER BY Checkintime) FROM DeviceHeartbeat WHERE DeviceId = 1112 ), x AS ( SELECT d = DATEDIFF(MINUTE, t1.Checkintime, t2.Checkintime) FROM t AS t1 INNER JOIN t AS t2 ON t1.rn = t2.rn - 1 ), y AS ( SELECT stats = CASE WHEN d &lt; 10 THEN ' &lt; 10 ' WHEN d BETWEEN 10 AND 11 THEN '10 - 11 ' WHEN d BETWEEN 11 AND 12 THEN '11 - 12 ' ELSE '+12 ' END + ' minutes:' FROM x ) SELECT stats, COUNT(*) FROM y GROUP BY stats; </code></pre> <p>This query is limited to a single specified device. Example results look like this:</p> <pre><code>stats ----------------- ---- &lt; 10 minutes: 1536 10 - 11 minutes: 425 11 - 12 minutes: 952 +12 minutes: 160 </code></pre> <p>Ideally, I’m only concerned with check-ins greater than 12 minutes. So, what I was wanting was a list of devices who have check-ins greater than 12 minutes, ordered by their counts. This will allow me to see the top 10 or 20 devices that have greater than 12 minute check-in times, alerting me to problem devices. Something like:</p> <pre><code>DeviceId CheckinsOver12Mins ---------- ------------------- 1112 160 1108 152 15 114 106 86 </code></pre> <p>Suggestions?</p>
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