Capture start and end times for changes of state o

Question

This is a variation of this question T-SQL Start and end date times from a single column except the event states may have multiple on or off states without a matching opposite state.

The question is how do I capture the start and end dates for the first "on" and next "off". In other words, capture the first COS (change of state) to "on" and the first COS to "off" for each item. This would be used to calculate a total runtime for the item.

Source:

Item      EventDate               Event
A         2011-10-03 00:01:00     On
A         2011-10-03 00:01:15     On
B         2011-10-03 00:01:00     On
A         2011-10-03 00:02:00     Off
A         2011-10-03 00:02:01     Off
C         2011-10-03 00:01:00     On
B         2011-10-03 00:02:00     Off
A         2011-10-03 00:02:02     On      
C         2011-10-03 00:02:05     On
A         2011-10-03 00:02:07     Off

Output:

Item      Start                   End
A         2011-10-03 00:01:00     2011-10-03 00:02:00
A         2011-10-03 00:02:02     2011-10-03 00:02:07
B         2011-10-03 00:01:00     2011-10-03 00:02:00
C         2011-10-03 00:01:00     2011-10-03 00:02:05

Answer 1

If you have SQL Server 2012 or later then you can use SQL Servers windowing function to get the desired results as follow:

CREATE TABLE [dbo].[EventStates](
    [Item] [varchar](1) NOT NULL,
    [EventDate] [varchar](19) NOT NULL,
    [Event] [varchar](3) NOT NULL
) ON [PRIMARY]

GO

INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'A', N'2011-10-03 00:01:00', N'On')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'A', N'2011-10-03 00:01:15', N'On')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'B', N'2011-10-03 00:01:00', N'On')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'A', N'2011-10-03 00:02:00', N'Off')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'A', N'2011-10-03 00:02:01', N'Off')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'C', N'2011-10-03 00:01:00', N'On')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'B', N'2011-10-03 00:02:00', N'Off')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'A', N'2011-10-03 00:02:02', N'On')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'C', N'2011-10-03 00:02:05', N'On')
INSERT [dbo].[EventStates] ([Item], [EventDate], [Event]) VALUES (N'A', N'2011-10-03 00:02:07', N'Off')

GO

;WITH StateChange
AS
(
    SELECT   E.[Item]
            ,E.[EventDate]
            ,E.[Event]
            ,(  -- First determine if a state change to on has occurred.
                CASE
                    WHEN E.[Event] = 'On' AND LAG(E.[Event], 1, NULL) OVER (PARTITION BY E.[Item] ORDER BY E.[EventDate] ASC) IS NULL THEN 1
                    WHEN E.[Event] = 'On' AND E.[Event] <> LAG(E.[Event], 1, NULL) OVER (PARTITION BY E.[Item] ORDER BY E.[EventDate] ASC) THEN 1
                    ELSE 0
                END
             ) [StateChanged]
    FROM    EventStates E
), StateChangeGrouping
AS
(
    SELECT   [Item]
            ,[EventDate]
            ,[Event]
            ,[StateChanged]
            ,SUM([StateChanged]) OVER (PARTITION BY [Item] ORDER BY [EventDate] ASC) AS [GroupID]
    FROM    StateChange 
), StateChangeRanked
AS
(
    SELECT   [Item]
            ,[EventDate]
            ,[Event]
            ,[StateChanged]
            ,[GroupID]
            ,ROW_NUMBER() OVER (PARTITION BY [Item], GroupID, [Event] ORDER BY [EventDate]) AS TransitionRank
    FROM    StateChangeGrouping
)
SELECT      [Item]
            ,MIN([EventDate]) AS [Start]
            ,MAX([EventDate]) AS [End]
            ,[GroupID]
FROM        StateChangeRanked
WHERE       GroupID > 0 AND TransitionRank = 1
GROUP BY    [Item], GroupID
ORDER BY    [Item], [Start]

Below is an implementation for SQL Server 2008.

;WITH EventID
AS
(
    SELECT   ROW_NUMBER() OVER(PARTITION BY [Item] ORDER BY [EventDate]) RowNr
            ,[Item]
            ,[EventDate]
            ,[Event] 
    FROM    [dbo].[EventStates]
), StateChange
AS
(
    SELECT  C.RowNr
            ,P.RowNr AS P_RowNr
            ,C.[Item]
            ,C.[EventDate]
            ,C.[Event] 
            ,P.[Event] AS P_Event
            ,(  -- First determine if a state change to on has occurred.
                CASE
                    WHEN C.[Event] = 'On' AND P.[Event] IS NULL THEN 1
                    WHEN C.[Event] = 'On' AND C.[Event] <> P.[Event] THEN 1
                    ELSE 0
                END
                ) [StateChanged]
    FROM    EventID C
    LEFT OUTER JOIN EventID P ON C.Item = P.Item AND C.RowNr = P.RowNr + 1
), StateChangeGrouping
AS
(
    SELECT   ST1.[Item]
            ,ST1.[EventDate]
            ,ST1.[Event]
            ,ST1.[StateChanged]
            ,(
                SELECT SUM([StateChanged])
                FROM StateChange ST2
                WHERE ST2.Item = ST1.Item AND ST2.RowNr <= ST1.RowNr
             ) AS GroupID
    FROM    StateChange ST1
), StateChangeRanked
AS
(
    SELECT   [Item]
            ,[EventDate]
            ,[Event]
            ,[StateChanged]
            ,[GroupID]
            ,ROW_NUMBER() OVER (PARTITION BY [Item], GroupID, [Event] ORDER BY [EventDate]) AS TransitionRank
    FROM    StateChangeGrouping
)
SELECT      [Item]
            ,MIN([EventDate]) AS [Start]
            ,MAX([EventDate]) AS [End]
            ,[GroupID]
FROM        StateChangeRanked
WHERE       GroupID > 0 AND TransitionRank = 1
GROUP BY    [Item], GroupID
ORDER BY    [Item], [Start]