Question

I have several tables:

lecturer(id,name,email)
- 1,john,[e-mail]
- 2,andy,[e-mail]
- 3,kyle,[e-mail]
- 4,allen,[e-mail]

sig(id,name)
- s1, Multimedia
- s2, Business IT

expertise(id, description); 
- e1, Gaming
- e2, Graphic
- e3, Multimedia System
- e4, E-Business

lecturer_has_expertise(lecturer.id,expertise.id)
- 1, e1
- 2, e2
- 3, e4
- 4, e1

lecturer_has_sig (lecturer.id,sig.id)
- 1, s1
- 2, s1
- 3, s2

sig_has_expertise(sig.id,expertise.id)
- s1, e1
- s1, e2
- s1, e3
- s2, e4

Here is the output I want to show:

Lecturer's Name, Email, Expertise

Basically, when a user inputs a keyword eg: Gaming into the textbox, it will show which lecturer’s expertise is gaming and since Gaming is under Multimedia,data about all lecturer in the sig of Multimedia also will be shown. For example:

Name   Email            Expertise
John   [e-mail]     Gaming
Allen  [e-mail]    Gaming
Andy   [e-mail]     Graphic    

I manage to output only the expertise that is input by the user but not all the expertise in the same sig.

thanks in advance

Answer 1

So basically you want to return every teacher who either

• has the specified expertise

  or

• belongs to a group that has the specified expertise.

This is how the above translates in SQL:

SELECT
  l.name,
  l.email,
  e.description AS expertise
FROM lecturer_has_expertise le
  INNER JOIN lecturer l ON l.id = le.lecturer_id
  INNER JOIN expertise e ON e.id = le.expertise_id
WHERE e.description = @InputExpertise
   OR EXISTS (
     SELECT *
     FROM lecturer_has_sig ls
       INNER JOIN sig_has_expertise se ON ls.sig_id = se.sig_id
       INNER JOIN expertise e ON e.id = se.expertise_id
     WHERE e.description = @InputExpertise
       AND ls.lecturer_id = le.lecturer_id
   )