Sql Server group by sets of columns - sql

Question

I have a data set where I need to count patient visits with such rules:
Two or more visits to the same doctor in the same day count as 1 visit, regardless of the reason
Two or more visits to different doctors for the same reason count as 1 visit
Two or more visits to different doctors on the same day for different reasons count as two or more visits.
Example data:
DoctorId PatientId VisitDate ReasonCode RowId
-------- --------- --------- ---------- -----
1 100 2014-01-01 200 1
1 100 2014-01-01 210 2
2 100 2014-01-01 200 3
2 100 2014-01-11 300 4
1 100 2014-01-15 200 5
2 400 2014-01-15 200 6
In this example, my final count would be based on grouping rowId 1, 2, 3 for 1 visit; grouping row 4 as 1 visit, grouping row 5 as 1 visit for a total of 3 visits for patient 100. Patient 400 has 1 visit as well.
patientid visitdate numberofvisits
--------- --------- --------------
100 2014-01-01 3
100 2014-01-11 1
100 2014-01-15 1
400 2014-01-15 1
Where I'm stuck is how to handle the group by so that I get the different scenarios covered. If the grouping were doctor, date, I'd be fine. If it were doctor, date, ReasonCode, I'd be fine. It's the logic of the doctorId and the ReasonCode in the scenario where 2 doctors are involved, and doctorid and date in the other when it's the same doctor. I've not been deeply into Sql Server in a long time, so it's possible that a common table expression is the solution and I'm not seeing it. I'm using Sql Server 2014 and there's a decent lattitude in performance. I would be looking for a sql server query that produces the results above. As best I can tell, there's no way to group this the way I need it counted.

Answer 1

The answer was an except clause and grouping each of the sets before a final count. Sometimes, we over-complicate things.
DECLARE #tblAllData TABLE
(
DoctorId INT NOT NULL
, PatientId INT NOT NULL
, VisitDate DATE NOT NULL
, ReasonCode INT NOT NULL
, RowId INT NOT NULL
)
INSERT #tblAllData
SELECT
1,100,'2014-01-01',200,1
UNION ALL
SELECT
1,100,'2014-01-01',210,2
UNION ALL
SELECT
2,100,'2014-01-01',200,3
UNION ALL
SELECT
2,100,'2014-01-11',300,4
UNION ALL
SELECT
1,100,'2014-01-15',200,5
UNION ALL
SELECT
2,400,'2014-01-15',200,6
DECLARE #tblTempCountedRows AS TABLE
(
PatientId INT NOT NULL
, VisitDate DATE
, ReasonCode INT
)
INSERT #tblTempCountedRows
SELECT PatientId, VisitDate,0
FROM #tblAllData
GROUP BY PatientId, DoctorId, VisitDate
EXCEPT
SELECT PatientId, VisitDate, ReasonCode
FROM #tblAllData
GROUP BY PatientId, VisitDate, ReasonCode
select * from #tblTempCountedRows
DECLARE #tblFinalCountedRows AS TABLE
(
PatientId INT NOT NULL
, VisitCount INT
)
INSERT #tblFinalCountedRows
SELECT
PatientId
, count(1) as Member_visit_Count
FROM
#tblTempCountedRows
GROUP BY PatientId
SELECT * from #tblFinalCountedRows
Here's a Sql Fiddle with the results:
Sql Fiddle