Select count from another table to each row in result rows

Question

Here are the tables:

CREATE TABLE [dbo].[Classes](
    [ClassId] [int] NOT NULL,
    [ClassName] [nvarchar](50) NOT NULL,
 CONSTRAINT [PK_Classes] PRIMARY KEY CL         


        

Answer 1

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]

Answer 2

Without having to add the group by clause, you can do the following:

Create a function to get the students count:

go
CREATE FUNCTION [dbo].GetStudentsCountByClass(@classId int) RETURNS INT
AS BEGIN
    declare @count as int

    select @count = count(*) from STUDENTS  
    where ClassId = @classId

    RETURN @count
END

then use it in your select statement

SELECT * , dbo.GetStudentsCountByClass(ClassId) AS StudentsCount
FROM Classes

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

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

Answer 5

 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