Ghi lại thời gian bắt đầu và kết thúc để biết các thay đổi về trạng thái của một trường

Nếu bạn có SQL Server 2012 trở lên thì bạn có thể sử dụng chức năng cửa sổ Máy chủ SQL để nhận được kết quả mong muốn như sau:

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]

Dưới đây là một triển khai cho 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]