Question

I created the tables like this:

create table utilisateur(
 id_util number(10) primary key,
 nom varchar2(10) not null,
 prenom varchar2(10) not null,
 date_naissance date not null,
 adress varchar2(20)
);

create table cour(
 id_cour number(10) primary key,
 c_nom varchar2(20) not null,
 auteur varchar2(20) not null
);

create table etude(
 fk_util number(10) references utilisateur(id_util),
 fk_cour number(10) references cour(id_cour),
 primary key(fk_util,fk_cour)
);

create table examen(
 id_ex number(10) primary key,
 ex_nom varchar2(20) not null,
 temp date,
 fk_cour number(10) references cour(id_cour)
);

create table passer(
 fk_util number(10) references utilisateur(id_util),
 fk_ex number(10) references examen(id_ex),
 primary key(fk_util,fk_ex),
 note number(4)
);

create table certificat(
 cert_nom varchar2(20),
 prix varchar2(10),
 code varchar2(10) primary key,
 fk_ex number(10),
 fk_util number(10)
);

create table signet(
 id_sign number(10) primary key,
 s_nom varchar2(20) not null,
 depand_par varchar2(20) not null,
 fk_util number(10) references utilisateur(id_util)
);

The problem is that I want to see all the users(utilisateur), which course(cour) they are reading, which exam(examen) they have passed and what certificates(certificat) they have received.

I have tried to do this with inner join, left and right join, full join, view, but without success. If I have 3 courses enregistrated and 2 exams, than I see something repeating. I’m thinking maybe in my database something is wrong.

Answer 1

This query

select utilisateur.nom
       , cour.c_nom
       , examen.ex_nom
from utilisateur left join etude on utilisateur.id_util=etude.fk_util 
left join cour on etude.fk_cour=cour.id_cour 
left join passer on utilisateur.id_util=passer.fk_util 
left join examen on passer.fk_ex=examen.id_ex;

Doesn’t take into account the fact that an exam is related to a course. I don’t think its necessary to do an outer join for what you are trying to achieve, so try this.

select utilisateur.nom
     , cour.c_nom
     , examen.ex_nom
from utilisateur join etude on utilisateur.id_util=etude.fk_util 
                 join cour on etude.fk_cour=cour.id_cour 
                 join passer on utilisateur.id_util=passer.fk_util 
                 join examen on cour.id_cour = examen.fk_cour;

Edit : This was a bit more complicated than it first appeared to me, I’ve added a new solution below. The first thing I did was add some aliases to the query, there is an issue with doing ansi joins between 3 or more tables if you don’t use aliases on certain versions of oracle. Aliases being generally a good thing, I’ve added them in anyway. I also moved some of the tables into inline views, to make the problem clearer to myself as much as anything. Aside from this tidying up, the only real change I’ve made is to add this line :-

AND paex.id_ex = coex.id_ex

I’ve tested this query against some data that I created as you described, and it seems to do what you want.

    SELECT ut.id_util
  ,ut.nom
  ,coex.c_nom
  ,paex.id_ex
  ,paex.ex_nom FROM   utilisateur ut LEFT JOIN (SELECT c_nom
             ,ex_nom
             ,co.id_cour
             ,id_ex 
             ,et.fk_util               
       FROM etude et JOIN cour co ON et.fk_cour = co.id_cour
                LEFT JOIN examen ex2 ON co.id_cour = ex2.fk_cour) coex ON coex.fk_util = ut.id_util LEFT JOIN (SELECT *
       FROM passer pa JOIN examen ex  ON pa.fk_ex   = ex.id_ex) paex ON paex.fk_util = ut.id_util 
                                                                    AND paex.id_ex = coex.id_ex ORDER BY id_util;