SQL Left Join (Multiple Join Condition)

Question

I have two derived tables named Check Ins and Check Outs

Check Ins

CheckDate  CheckIn
---------- ---------
08/02/2011 10:10:03
08/02/2011 15:57:16
07/19/2011 13:58:52
07/19/2011 16:50:55
07/26/2011 15:11:24
06/21/2011 12:36:47
08/16/2011 14:49:36
08/09/2011 13:52:10
08/09/2011 16:54:51
08/23/2011 15:48:58
09/06/2011 15:23:00
09/13/2011 10:09:27
09/13/2011 10:40:14
09/13/2011 11:43:14
09/13/2011 11:59:32
09/13/2011 17:05:24
09/20/2011 11:03:42
09/20/2011 12:08:50
09/20/2011 15:21:06
09/20/2011 15:34:29
09/27/2011 11:34:06
10/04/2011 11:37:59
10/04/2011 15:24:04
10/04/2011 16:57:44
10/11/2011 18:19:33

Check Outs

CheckDate  CheckOut
---------- ---------
08/02/2011 13:29:40
08/02/2011 17:02:25
07/12/2011 17:06:06
07/19/2011 16:40:15
07/19/2011 17:07:35
07/26/2011 14:48:10
07/26/2011 17:27:08
05/31/2011 17:01:39
06/07/2011 17:04:29
06/14/2011 17:08:50
06/21/2011 17:03:46
06/28/2011 17:10:45
07/05/2011 17:02:48
08/16/2011 13:37:36
08/16/2011 17:06:34
08/09/2011 12:00:29
08/09/2011 13:29:36
08/09/2011 14:36:09
08/09/2011 17:00:38
08/23/2011 13:37:11
08/23/2011 17:01:37
09/06/2011 17:00:09
09/13/2011 10:11:50
09/13/2011 11:22:02
09/13/2011 11:47:35
09/13/2011 14:13:36
09/13/2011 14:14:25
09/13/2011 17:08:43
09/20/2011 09:54:55
09/20/2011 11:55:31
09/20/2011 11:55:36
09/20/2011 13:35:16
09/20/2011 15:26:02
09/20/2011 16:33:21
09/20/2011 17:07:52
09/27/2011 11:12:38
10/04/2011 13:26:31
10/04/2011 16:32:56
10/04/2011 17:02:35
10/11/2011 18:25:32

I want to pair the check ins with the check outs given the condition that both logs are on the same date and check out values cannot be earlier than check ins, so I have come up with this query

  SELECT A.ChkDt
      AS CheckDate,
         B.CheckIn,
         MIN(A.ChkTm)
      AS CheckOut
    FROM #tempAttLogs
      AS A LEFT JOIN
         (SELECT ChkDt
              AS CheckDate,
                 MIN(ChkTm)
              AS CheckIn
            FROM #tempAttLogs
           WHERE ChkTp = 'I'
        GROUP BY ChkDt) B
      ON A.ChkDt = B.CheckDate
   WHERE ChkTp = 'O' AND
         A.ChkTm > B.CheckIn
GROUP BY A.ChkDt, B.CheckIn

With a result set of

CheckDate  CheckIn   CheckOut
---------- --------- ---------
06/21/2011 12:36:47  17:03:46
07/19/2011 13:58:52  16:40:15
07/26/2011 15:11:24  17:27:08
08/02/2011 10:10:03  13:29:40
08/09/2011 13:52:10  14:36:09
08/16/2011 14:49:36  17:06:34
08/23/2011 15:48:58  17:01:37
09/06/2011 15:23:00  17:00:09
09/13/2011 10:09:27  10:11:50
09/20/2011 11:03:42  11:55:31
10/04/2011 11:37:59  13:26:31
10/11/2011 18:19:33  18:25:32

The thing is I also want to include the logs with no corresponding pairs. How can this be possible?

EDIT

My expected result set must include logs like this

CheckDate  CheckIn   CheckOut
---------- --------- ---------
05/23/2011 NULL      17:04:27

Answer 1

You can move any predicate referencing the right hand table into the ON clause instead of the WHERE to avoid turning the JOIN into an INNER JOIN

e.g.

ON A.ChkDt = B.CheckDate AND
         A.ChkTm > B.CheckIn
WHERE ChkTp = 'O'

Instead of

    ON A.ChkDt = B.CheckDate
   WHERE ChkTp = 'O' AND
         A.ChkTm > B.CheckIn

Answer 2

Include the null values in your WHERE clause Ex:

WHERE( ChkTp = 'O' AND
         A.ChkTm > B.CheckIn) OR B.CheckDate IS NULL

Answer 3

This might be useful (not tested) to solve your problem though it is at a slight tangent to your question.

select 
  Checkdate, CheckIn as CheckTime, 'I' as CheckAction
from CheckIns 

union all

select 
  Checkdate, CheckOut as CheckTime, 'O' as CheckAction
from CheckOuts
order by 1,2