按消息类型对行进行分组，每个消息组之间的持续时间以分钟为单位

Question

I have a table that stores messages for a host, I am trying to group the messages by type and show the amount of minutes they occurred for. I need to show the minimum message date and the maximum message date for each group. I have the following query and I am able to get the messages to group by type with the min time and message time, however I need the min time to be the max time of the previous row.

;WITH cte as (
SELECT CRS, WindowNumber, StateOfServiceReason,  DateOfEntry, 
ROW_NUMBER() OVER(PARTITION BY StateOfServiceReason ORDER BY CRS, Windownumber, DateOfEntry) AS gn,
ROW_NUMBER() OVER (ORDER BY CRS, WindowNumber, DateOfEntry) AS rn
FROM [dbo].[ServiceLog]
WHERE       1 = 1
AND         CRS = 'BBP'
AND         WindowNumber = 1), cte2 AS (
SELECT CRS, WindowNumber, StateOfServiceReason, DateOfEntry, gn, rn, gn - rn as gb
FROM cte ) , cte3 AS (
SELECT CRS, WindowNumber,StateOfServiceReason, MIN(DateOfEntry) AS MinMsgDate, MAX(DateOfEntry) As MaxMsgDate,
DATEDIFF(MINUTE, MIN(DateOfEntry), Max(DateOfEntry)) as TotalMinutes
FROM cte2
GROUP BY CRS, WindowNumber,StateOfServiceReason, gb)

My output looks like this:

CRS WindowNumber    StateOfServiceReason    MinMsgDate          MaxMsgDate      TotalMinutes
BBP 1               Unknown                 2017-07-01 00:07:46 2017-07-01 02:47:05 160
BBP 1               OperatorMaintenance     2017-07-01 02:47:05 2017-07-01 03:01:10 0
BBP 1               Unknown                 2017-07-01 03:01:10 2017-07-01 08:37:26 336
BBP 1               OperatorMaintenance     2017-07-01 08:37:26 2017-07-01 18:36:14 598

I would like it to like this

CRS WindowNumber    StateOfServiceReason    MinMsgDate          MaxMsgDate          TotalMinutes
BBP 1               Unknown                 01/07/2017 00:07:46 01/07/2017 02:47:06 xx
BBP 1               OperatorMaintenance     01/07/2017 02:47:06 01/07/2017 03:01:10 xx
BBP 1               Unknown                 01/07/2017 03:01:10 01/07/2017 08:37:27 xx
BBP 1               OperatorMaintenance     01/07/2017 08:37:27 01/07/2017 18:36:14 xx

I have been playing around with the query for a while now and any help would be appreciated.

Answer 1

In sqlserver, the window function LAG(column) OVER(order by x) can be used to return the value of column in a previous row, where the ORDER BY x defines what would be the "previous" row. Bear in mind you might want to also PARTITION BY your_grouping to ensure the first row from a group doesn't pull a previous value from another group