Delete rows following a duplicate

I have a list of user login and logout stamps. Unfortunately a LOGIN entry might not always be followed by a LOGOUT entry.

I wish to delete any row which has the same [event] and [user_id] as previous row when ordered by [event_date] Any suggestions on how to do this?

Example table

CREATE TABLE #LOG (
    [id] int IDENTITY(1,1),
    [user_id] int,
    [event] varchar(50),
    [event_date] datetime
);
INSERT INTO #LOG ([user_id], [event], [event_date])
SELECT 1,'LOGIN',{ts '2010-12-15 15:31:59'}
UNION ALL SELECT 1,'LOGOUT',{ts '2010-12-15 15:32:55'}
UNION ALL SELECT 1,'LOGIN',{ts '2010-12-15 15:38:04'}
UNION ALL SELECT 1,'LOGOUT',{ts '2010-12-15 15:38:17'}
UNION ALL SELECT 1,'LOGOUT',{ts '2010-12-1开发者_StackOverflow5 15:38:45'} -- Delete
UNION ALL SELECT 2,'LOGIN',{ts '2010-12-15 16:59:39'}
UNION ALL SELECT 2,'LOGOUT',{ts '2010-12-15 17:00:08'}
UNION ALL SELECT 2,'LOGOUT',{ts '2010-12-15 17:00:39'} -- Delete
UNION ALL SELECT 2,'LOGOUT',{ts '2010-12-15 17:01:16'} -- Delete
UNION ALL SELECT 2,'LOGIN',{ts '2010-12-15 17:01:38'}
UNION ALL SELECT 2,'LOGIN',{ts '2010-12-15 17:02:26'} -- Delete
UNION ALL SELECT 2,'LOGOUT',{ts '2010-12-15 17:02:39'}

;WITH T1 AS
(
SELECT * , 
        ROW_NUMBER() OVER (ORDER BY event_date)-
        ROW_NUMBER() OVER (PARTITION BY [user_id], [event] 
                               ORDER BY event_date) AS Grp
FROM #LOG
),T2 AS
(
SELECT 
   ROW_NUMBER() OVER (PARTITION BY [user_id], [event], Grp 
                          ORDER BY event_date) RN
FROM T1
)
DELETE FROM T2 
WHERE RN > 1

Using the ROW_NUMBER functionality of SQL Server would be an option

SQL Statement

;WITH q AS (
    SELECT  Rownumber = ROW_NUMBER() OVER (ORDER BY user_id, event_date)
    , user_id
    , event
    , event_date
    FROM    #LOG
)
DELETE FROM #LOG
FROM    #LOG l
        INNER JOIN (
            SELECT  q2.*
            FROM    q q1
                    INNER JOIN q q2 ON  q2.Rownumber = q1.Rownumber + 1
                                        AND q2.user_id = q1.user_id
                                        AND q2.event = q1.event
        ) q ON  q.user_id = l.user_id
                AND q.event_date = l.event_date

SELECT  *
FROM    #LOG

My understanding is that you want to delete entries such that the pattern is always In,Out,In,Out,etc.

This means a record is deleted if the preceding record (when order by user_id, then event_date), is of the same event.

There are two options I'd use to go about this...

DELETE
  #log
WHERE
  event = (
           SELECT
             TOP 1
             event
           FROM
             #log AS [preceding]
           WHERE
             [preceding].user_id = #log.user_id
             AND [preceding].event_date < #log.event_date
           ORDER BY
             [preceding].event_date DESC
          )

Or...

WITH ordered_log AS (
  SELECT
    ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY event_date) AS user_event_id,
    *
  FROM
    #log
)

DELETE
  ordered_log
FROM
  ordered_log
INNER JOIN
  ordered_log   AS [preceding]
    ON  [preceding].login_id      = [ordered_log].login_id
    AND [preceding].user_event_id = [ordered_log].user_event_id - 1
WHERE
  [preceding].event = [ordered_log].event

Either way, I highly recommend an Index covering user_id then event_date.

Note: The first version does not cope with the possibility of two events having the same timestamp. The latter, however, does.

If you have to delete duplicate row. Then no need to set the order by clause.

Try below

Delete l from #LOG l
Inner Join 
(
    Select id from #LOG l
    Inner Join(
        Select user_id, event from #LOG 
        group by user_id, event
        having COUNT(user_id) > 1 and COUNT(event) > 1
    )T
    on (l.user_id = t.user_id) and (l.event = t.event)
)T
on T.id = l.id