SQL Query Problem -- Are Pivots Necessary?

Question

Given the following data:

CardholderID   Source                                   DateTime
-------------- ---------------------------------------- -----------------------
3              2nd_Flr_Ramp_Out_Reader                  2010-06-30 13:58:42.410
3              2nd_Flr_Ramp_In_Reader                   2010-06-30 13:44:22.417
3              2nd_Flr_Ramp_Out_Reader                  2010-06-30 13:41:30.510
3              Lobby_To_Office_Reader                   2010-06-30 13:27:51.407
3              2nd_Flr_Ramp_Out_Reader                  2010-06-30 13:27:31.313
3              2nd_Flr_Ramp_In_Reader                   2010-06-30 13:27:23.203
3              2nd_Flr_Ramp_Out_Reader                  2010-06-29 12:03:04.413
3              2nd_Flr_Ramp_In_Reader                   2010-06-29 09:18:16.417
3              2nd_Flr_Ramp_Out_Reader                  2010-06-28 17:51:08.507
3              2nd_Flr_Ramp_In_Reader                   2010-06-28 12:52:28.403
3              2nd_Flr_Ramp_Out_Reader                  2010-06-28 12:04:36.407
3              2nd_Flr_Ramp_In_Reader                   2010-06-28 09:17:20.407
4              1St_Flr_To_Stairs_Reader                 2010-08-02 09:41:14.403
4              1St_Flr_Door_In_Reader                   2010-08-02 09:41:12.403
4              1St_Flr_Door_Out_Reader                  2010-07-30 18:24:36.400
4              1St_Flr_To_Stairs_Reader                 2010-07-30 14:09:54.403
4              1St_Flr_Door_In_Reader                   2010-07-30 14:09:48.403
4              1St_Flr_Door_Out_Reader                  2010-07-30 13:25:24.407

How can I obtain the minimum time for an "In" source and the maximum time for an "Out" source for each cardholderId by day.

The first thing I tried was

select CardHolderId, min(DateTime) as EarliestSwipe, null as LatestSwipe
from EventTable
where source like '%In_Reader%'
group by cardholderid, CardHolderFirstName, CardHolderLastName,dateadd(dd, (datediff(dd, 0, DateTime)),0)
union 
select CardHolderId, null as EarliestSwipe, max(DateTime) as LatestSwipe
from EventTable
where source like '%Out_Reader%'
group by cardholderid, CardHolderFirstName, CardHolderLastName, dateadd(dd, (datediff(dd, 0, DateTime)),0)

but I need the results of the two queries combined. My question is, do I need to pivot the data to get the results that I desire or can I remain on the track of the example I provided. I would greatly appreciate any assistance.

Answer 1

Give this a try.

SELECT CardholderID,
    MIN(CASE WHEN source like '%In_Reader%' THEN DateTime ELSE NULL END) as EarliestSwipe,
    MAX(CASE WHEN source like '%Out_Reader%' THEN DateTime ELSE NULL END) as LatestSwipe,
FROM EventTable
GROUP BY CardholderID

I excluded your additional GROUP BY values, but I think they can be added.