Merge Overlapping Date Ranges in SQL Server

Merge overlapping date ranges

DECLARE @T table (GroupSourceID varchar(100), EmployeeID VARCHAR(100),  StartDate  datetime,  EndDate datetime);
insert into @T values
 ('Green', '1'   , '2017-01-02 00:00' , '2017-03-28 00:10'),
 ('Green', '1'   , '2017-05-14 23:50' , '2017-05-29 23:50'),
 ('Green', '1'   , '2017-04-14 23:50' , '2018-05-29 23:50'),
 ('Yellow', '2'   , '2017-05-18 00:00' , '2017-05-18 04:00'),
 ('Yellow', '2'   , '2017-05-18 02:00' , '2017-05-18 03:00'),
 ('Yellow', '1'   , '2017-05-18 02:00' , '2017-05-18 03:00'),
 ('Blue', '1', '2017-01-02 00:00' , '2017-01-17 15:50'),
 ('Blue', '1', '2017-01-12 00:00' , '2017-02-17 15:50'),
 ('Blue', '3' , '2017-01-14 03:50' , '2017-01-28 15:50'),
 ('Blue', '3' , '2018-01-14 03:50' , '2018-01-28 15:50');

 --SELECT * FROM @T;

WITH StartDates AS 
( 
  SELECT DISTINCT GroupSourceID, EmployeeID, StartDate 
	FROM @T AS T1 
  WHERE NOT EXISTS 
    (SELECT * FROM @T AS T2 
     WHERE T1.GroupSourceID = T2.GroupSourceID AND T1.EmployeeID = T2.EmployeeID
       AND T2.StartDate < T1.StartDate 
       AND T2.EndDate >= T1.StartDate) 
), 
EndDates AS 
( 
  SELECT DISTINCT GroupSourceID, EmployeeID, EndDate 
  FROM @T AS T1 
  WHERE NOT EXISTS 
    (SELECT * FROM @T AS T2 
     WHERE T1.GroupSourceID = T2.GroupSourceID AND T1.EmployeeID = T2.EmployeeID
       AND T2.EndDate > T1.EndDate 
       AND T2.StartDate <= T1.EndDate) 
) 
SELECT GroupSourceID,  EmployeeID,
       StartDate, 
      (SELECT MIN(EndDate) 
       FROM EndDates AS E 
       WHERE E.GroupSourceID = S.GroupSourceID AND E.EmployeeID = S.EmployeeID
         AND EndDate >= StartDate) AS EndDate 
FROM StartDates AS s;

Obtained solution from this Stack Overflow question.

https://stackoverflow.com/questions/48425120/merge-overlapping-dates-in-sql-server