join status history - sql

Question

I have a table listing patient days for encounters. Below a sample for one encounter. Every day the patient is in the hospital one record is created at midnight untill discharge.
Enc_iD Day_Id ServiceDtTm AdmitDate
2616350 34707672 2/21/2013 23:59 21/FEB/13 12:19:00
2616350 34733898 2/22/2013 23:59 21/FEB/13 12:19:00
2616350 34748155 2/23/2013 23:59 21/FEB/13 12:19:00
2616350 34760403 2/24/2013 23:59 21/FEB/13 12:19:00
2616350 34784357 2/25/2013 23:59 21/FEB/13 12:19:00
2616350 34808228 2/26/2013 23:59 21/FEB/13 12:19:00
2616350 34814512 2/27/2013 10:10 21/FEB/13 12:19:00
In a separate table a status for every encounter is maintained irregulary by a user.
Enc_iD TransDtTm Status
2616350 2/21/2013 12:20
2616350 2/21/2013 13:29 1
2616350 2/22/2013 7:28 3
2616350 2/25/2013 13:44 2
2616350 2/27/2013 10:10 2
I want to create a resultset with SQL as below. So for every day in the top table the status that was the most recent at that ServiceDtTm.
Enc_iD Day_Id DtTime AdmitDate Status
2616350 34707672 2/21/2013 23:59 21/FEB/13 12:19:00 1
2616350 34733898 2/22/2013 23:59 21/FEB/13 12:19:00 3
2616350 34748155 2/23/2013 23:59 21/FEB/13 12:19:00 3
2616350 34760403 2/24/2013 23:59 21/FEB/13 12:19:00 3
2616350 34784357 2/25/2013 23:59 21/FEB/13 12:19:00 2
2616350 34808228 2/26/2013 23:59 21/FEB/13 12:19:00 2
2616350 34814512 2/27/2013 10:10 21/FEB/13 12:19:00 2
Any help is appreciated. Can't figure this out SQL. Only in excel by using vlookup with approximate match.
Robbert

Answer 1

I think the simplest solution is a correlated subquery. Here is the syntax in SQL Server:
select pd.*,
(select top 1 status
from status s
where s.enc_id = pd.enc_id and s.transdttm <= pd.servicedttm
order by s.transdttm
) as MostRecentStatus
from patientdays pd
For most other databases, it would look like:
select pd.*,
(select status
from status s
where s.enc_id = pd.enc_id and s.transdttm <= pd.servicedttm
order by s.transdttm
limit 1
) as MostRecentStatus
from patientdays pd