SELECT DISTINCT Course.ID1, STUFF((SELECT ',' + Name FROM Student s INNER JOIN Attendence a ON s.ID2 = a.ID2 WHERE a.ID1 = c.ID1 FOR XML PATH('')), 1, 1, '')
FROM Course c
SELECT DISTINCT c.ID1,
STUFF((SELECT ',' + Name2 FROM Student s INNER JOIN Attendance a ON s.ID2 = a.ID2 WHERE a.ID1 = c.ID1 FOR XML PATH('')), 1, 1, '')
FROM Course c