concat string many row to single row

SubjectID       StudentName

----------      -------------
1               Mary
1               John
1               Sam
2               Alaina
2               Edward

Result I expected was:

SubjectID       StudentName
----------      -------------
1               Mary, John, Sam
2               Alaina, Edward

I used the following T-SQL:

Select Main.SubjectID,
       Left(Main.Students,Len(Main.Students)-1) As "Students"
From(Select distinct ST2.SubjectID, 
           (Select ST1.StudentName + ',' AS [text()]
            From dbo.Students ST1
            Where ST1.SubjectID = ST2.SubjectID
            ORDER BY ST1.SubjectID
            For XML PATH ('')) [Students]
     From dbo.Students ST2) [Main]

http://stackoverflow.com/questions/194852/concatenate-many-rows-into-a-single-text-string

เอาค่าหลายๆ record มาต่อกันเป็น record เดียว