Question

I have a task that I’m getting a bit hung up on with SQL Server and wondered if anybody could help.

Task:
Within the database, I need to create a stored procedure with the name ClassRegistration. The columns of the result set for this stored procedure need to be as follows:

1. [Class] – The name of the class to be taught
2. [Teacher Name] – The name of the person teaching the class
3. [Registrations] – The number of pupils who have registered to take the class
4. [Number Paid] – The number of pupils who have paid their fees for the class

Tables:

1. [Teacher] : Teacher_ID (PK), TeacherName
2. [Class] : Class_ID (PK), ClassName, Teacher_ID (FK)
3. [ClassRegistration] Student_ID (FK), Class_ID (FK), HasPaidFees
4. [Student] Student_ID (PK), StudentName

The college needs to know about every class, even if nobody has yet registered.

My SQL so far:

Create  PROCEDURE ClassRegistration
AS
SELECT DISTINCT 
    c.ClassName, 
    t.TeacherName, 
    COUNT(cr.Student_ID) As Registrations, 
    COUNT(case when cr.HasPaidFees = 1 then 1 else null end) As NumberPaid
FROM 
    Class As c, 
    Teacher As t, 
    ClassRegistration As cr, 
    Student As s
WHERE
    (c.Class_ID = cr.Class_ID) 
AND (cr.Student_ID = s.Student_ID)
GROUP BY c.ClassName, t.TeacherName

I can create the stored procedure fine but the output doesn’t look correct, any help would be greatly appreciated :).

Answer 1

There is no reason to join to Student and you had 4 tables but only 2 join criteria. This is one of the pitfalls of using old table,table join syntax instead of proper, explicit joins. I also:

• listed your "inner" tables first
• added dbo. prefix to table references
• added SET NOCOUNT ON to the procedure
• removed the unnecessary DISTINCT
• simplified the CASE expression

CREATE PROCEDURE dbo.ClassRegistration
AS
BEGIN
  SET NOCOUNT ON;

  SELECT c.ClassName, t.TeacherName, 
    COUNT(cr.Student_ID) As Registrations, 
    COUNT(NULLIF(cr.HasPaidFees, 0)) As NumberPaid
  FROM dbo.Class As c
  INNER JOIN dbo.Teacher As t
  ON t.Teacher_ID = c.Teacher_ID
  LEFT OUTER JOIN dbo.ClassRegistration As cr
  ON c.Class_ID = cr.Class_ID
  GROUP BY c.ClassName, t.TeacherName;
END
GO