将sql转换为linq扩展方法带有select group by的内连接

var result = from s in students
             join c in courses on s.CourseID equals c.CourseID
             group s by c.CourseName into g
             select new { CourseName = g.Key, TotalStudents = g.Count() };

var result = students.Join(courses, 
                            s => s.CourseID, 
                            c => c.CourseID, 
                            (s, c) => new { Student = s, Course = c })
                    .GroupBy(x => x.Course.CourseName)
                    .Select(g => new { CourseName = g.Key, TotalStudents = g.Count() });