Calculate Time Difference Between Two Rows

Question

I have a table that contains the following:

DataDate                 Value 2010-03-01 08:31:32.000  100 2010-03-01 08:31:40.000  110 2010-03-01 08:31:42.000  95 2010-03-01 08:31:45.000  101 .                        . .                        . .                        . 

I need to multiply the value column by the difference in time between the current and previous rows and sum that for the entire day.

I currently have the data set up to come in every 10 seconds which makes for a simple conversion in the query:

SELECT Sum((Value/6) FROM History WHERE DataDate BETWEEN @startDate and @endDate 

Where @startDate and @endDate are today's date at 00:00:00 and 11:59:59.

Before I set the data to be collected every 10 seconds it was collected whenever the Value changed. There aren't any duplicate entries in terms of time, the minimum time difference is 1 second.

How can I set up a query to get the elapsed time between rows for the case when I don't know the time interval between readings?

I am using SQL Server 2005.

Answer 1

WITH    rows AS         (         SELECT  *, ROW_NUMBER() OVER (ORDER BY DataDate) AS rn         FROM    mytable         ) SELECT  DATEDIFF(second, mc.DataDate, mp.DataDate) FROM    rows mc JOIN    rows mp ON      mc.rn = mp.rn - 1 

In SQL Server 2012+:

SELECT  DATEDIFF(second, pDataDate, dataDate) FROM    (         SELECT  *,                 LAG(dataDate) OVER (ORDER BY dataDate) pDataDate         FROM    rows         ) q WHERE   pDataDate IS NOT NULL