Check the below input data and expected output to make the comma separated week aggregation for common schedules.

Input Data:

ScheduleID  StartDate  EndDate    WeekID
----------- ---------- ---------- ------
1           2017-01-08 2017-01-09 1
1           2017-01-08 2017-01-09 2
2           2017-02-08 2017-02-09 4
3           2017-04-08 2017-05-08 6
3           2017-04-08 2017-05-08 7
4           2017-02-10 2017-04-09 3

Expected Output:

ScheduleID  StartDate  EndDate    Weeks
----------- ---------- ---------- -------
4           2017-02-10 2017-04-09  3
3           2017-04-08 2017-05-08  6, 7
2           2017-02-08 2017-02-09  4
1           2017-01-08 2017-01-09  1, 2

Create a table with sample data:

CREATE TABLE Schedules  
(
	ScheduleID INT 
	,StartDate DATE
	,EndDate DATE
	,WeekID VARCHAR(2)	
) 
GO
 
INSERT INTO Schedules 
VALUES
(1,'2017-01-08','2017-01-09',1)
,(1,'2017-01-08','2017-01-09',2)
,(2,'2017-02-08','2017-02-09',4)
,(3,'2017-04-08','2017-05-08',6)
,(3,'2017-04-08','2017-05-08',7)
,(4,'2017-02-10','2017-04-09',3)
GO

Solution:

SELECT ScheduleID,StartDate, EndDate,
STUFF(( SELECT ', ' + t1.WeekID 
FROM Schedules  t1 
WHERE s.ScheduleID = t1.ScheduleID 
        AND s.StartDate = t1.StartDate 
        AND s.EndDate = t1.EndDate         
        FOR XML PATH('')), 1, 1, '') Weeks
FROM Schedules s
GROUP BY ScheduleID,StartDate,EndDate
ORDER BY ScheduleID DESC

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