Question

I have a table called Visits:

ID(PKey,Int)
PatiendID(int),
DoctorID(int),
ExpectedDate(date),
ActualDate(date),

How can I write a query that for each patient returns the numbers of repeat visits.

The visit is considered to be repeated if it is less then half of the year from previous visit.

In other words I need for each patient find number of visits between (last visit-6 months) and last visit excluding last visit. Is it possible to write a query without cursors?

And other question. I have Table Patients

ID(int, PKey),Name,Pasport,State

Is it possible for each client from here find the same information? Or it is better union the query below and all clients that are not in visits table?

Answer 1

In other words I need for each patient find number of visits between
(last visit-6 months) and last visit excluding last visit.

WITH CTE AS
(
    SELECT PatientID, MAX(ActualDate) AS LastVisit
    FROM Visits
    GROUP BY PatientID
)
SELECT CTE.PatientID, COUNT(1)-1 AS RepeatVisits
FROM CTE INNER JOIN Visits ON CTE.PatientID = Visits.PatientID
WHERE ActualDate BETWEEN DATEADD(month, -6, LastVisit) AND LastVisit
GROUP BY CTE.PatientId

This will group, by patient, all visits in the six months before the last visit. It will give you the COUNT (total) minus one (excluding the last visit).

Complete example: http://pastebin.com/vpCdASpB

For the second part (Patients table), see here: http://pastebin.com/nKw0Wqvp

WITH CTE AS
(
    SELECT Patients.PatientID, Patients.Name, MAX(ActualDate) AS LastVisit
    FROM Patients LEFT JOIN Visits ON #patient.PatientID = Visits.PatientID
    GROUP BY Patients.PatientID, Patients.Name
)
SELECT CTE.PatientID, CTE.Name, COUNT(1)-1 AS RepeatVisits
FROM CTE LEFT JOIN Visits ON CTE.PatientID = Visits.PatientID
                          AND Visits.ActualDate BETWEEN DATEADD(month, -6, LastVisit) AND LastVisit
GROUP BY CTE.PatientId, CTE.Name
ORDER BY PatientID;