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Select a counter from another table to each row in the result lines

Here are the tables:

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

I want to get a list of classes, and each class is the number of students belonging to each class. How can i do this?

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4 answers

You need to do this -

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
+17
source

Do you mean something like this?

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]
+2
source 
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
0
 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
0

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