Вот таблицы:

CREATE TABLE [dbo].[Classes](
    [ClassId] [int] NOT NULL,
    [ClassName] [nvarchar](50) NOT NULL,
 CONSTRAINT [PK_Classes] PRIMARY KEY CLUSTERED 
(
    [ClassId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Students](
    [StudentId] [int] NOT NULL,
    [ClassId] [int] NOT NULL,
 CONSTRAINT [PK_Students] PRIMARY KEY CLUSTERED 
(
    [StudentId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[Students]  WITH CHECK ADD  CONSTRAINT [FK_Students_Classes] FOREIGN KEY([ClassId])
REFERENCES [dbo].[Classes] ([ClassId])
GO
ALTER TABLE [dbo].[Students] CHECK CONSTRAINT [FK_Students_Classes]
GO

Я хочу получить список классов, а в каждом классе - количество учеников, которые принадлежат каждому классу. Как я могу это сделать?