Question

I have a question about an SQL I want to perform but got no idea on how to write it. Below are the tables with so dummy data:

Module:

ModuleId (PK auto) ModuleNo   ModuleName
1                  CHI2523    Business

Course:

CourseId (PK auto)  CourseName
1                    Business and Computing
2                    ICT
3                    Sports

Course_Module:

CourseId (PK) ModuleId (PK)
1             1 
2             1

Session:

SessionId (PK auto)  SessionName  ModuleId (FK)
3                    DFRER        1

Student:

StudentId (PK auto)  StudentAlias StudentForename  StudentSurname  CourseId (FK)
1                    u03824       Bill             Murphy          1
2                    u38492       Conrad           Jones           2
3                    u48383       Jane             Peters          1
4                    u34322       Morgan           Gray            2
5                    u39292       Bilal            Tuddy           3

Student_Session:

SessionId (PK)  StudentId (PK)
3               1
3               2

What I want the query to be able to find is all of the remaining students that are not currently taking the selected assessment but who are legible to take the assessment.

So to be able to do this we have to:

• Look at what the selected session is by looking up SessionId in Session Table

• See which module that SessionId belongs to by seeing the ModuleId in Session Table.

• See which courses that ModuleId is in by looking up Course_Module table

• Look up each student’s course by looking at CourseId in student table that matches with the CourseId‘s from the Course_Module Table

• Display all students who belongs to the Course where the module is in, but only dislay students who are not currently in the session (or in other words not in the Session Table taking the selected SessionId.

So if the SessionId chosen is 3, then the students it should output are:

StudentId (PK auto)  StudentAlias StudentForename  StudentSurname  CourseId (FK)
3                    u48383       Jane             Peters          1
4                    u34322       Morgan           Gray            2

This is because:

• SessionId 3 belongs to ModuleId 1

• ModuleId belongs to CourseId 1 and 2

• Looking up CourseId 1 and 2 there are 4 students who take that course

• But 2 of those students are already taking SessionId 3 when looking at Student_Session Table, so only display the other 2 students as they are currently not taking the session

My question is how is the query suppose to be written to be able to achieve the example mentioned above? I have made a start on the query but need someone’s help to enhance it so it meets with the repuirements of the example above:

SELECT s.StudentId, StudentAlias, StudentForename, StudentSurname
FROM Session s 
INNER JOIN Module m ON m.ModuleId = s.ModuleId
INNER JOIN Course_Module cm ON cm.ModuleId = m.ModuleId
INNER JOIN Student s ON cm.CourseId = s.CourseId
INNER JOIN Student_Session ss ON s.StudentId = ss.StudentId
WHERE s.SessionId = 3
ORDER BY StudentAlias;

I don’t know how to check to see which students are/are not legible and then selecting only those students who are legible for taking assessment but who are not currently taking part in assessment

Answer 1

SELECT  e.*
FROM    Session a
        INNER JOIN Module b
            ON a.ModuleID = b.ModuleID
        INNER JOIN Course_Module c
            ON b.ModuleID = c.ModuleID
        INNER JOIN Course d
            ON c.CourseID = d.CourseID
        INNER JOIN Student e
            ON d.CourseID = e.CourseID
        LEFT JOIN Student_Session f
            ON f.sessionID = a.SessionID AND
                f.studentID = e.studentID
WHERE   a.SessionID = 3 AND
        f.studentID IS NULL
ORDER   BY e.STUDENTALIAS

• SQLFiddle Demo