selezionare il conteggio da un altro tavolo a ciascuna riga righe di risultato

Question

Ecco i tavoli:

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 

voglio ottenere l'elenco di classe, e ogni classe - il numero di studenti che appartengono a ciascuna classe. Come posso fare questo?

Answer 1

Hai bisogno di fare questo -

SELECT C.ClassId, C.ClassName, count(S.StudentId) AS studentCount 
FROM CLASSES C LEFT JOIN STUDENTS S ON (C.ClassId=S.ClassId) 
GROUP BY C.ClassId, C.ClassName 

Answer 2

Vuoi dire qualcosa di simile?

SELECT C.[ClassName], COUNT(*) AS 'Number of Students' 
FROM [dbo].[Classes] AS C 
    INNER JOIN [dbo].[Students] AS S ON S.[ClassId] = C.[ClassId] 
GROUP BY C.[ClassName] 

Answer 3

SELECT class.ClassId, count(student .StudentId) AS studentCount 
FROM dbo.CLASSES class LEFT JOIN dbo.STUDENTS student ON (class.ClassId=student.ClassId) 
GROUP BY class.ClassId 

Answer 4

select c.ClassId,C.ClassName,COUNT(*) [Number of students] 
from Classes C,Students S 
where c.ClassId=S.ClassId 
group by C.ClassId,C.ClassName