Is there any other way to extract the number of exam? - php

Question

Hello everyone I have a problem that I need help with I'm trying to get number of exam for specified student
we have three tables :
etudient (N_Appoge,Nom,PRENOM,filiere,....)
module (NUM_Module,Nom_module,Nom_semestre)
Inscrit (N_Appoge,NUM_Module) // this table is the relation between etudiant & module
so basically students with the same class means they have the same filiere and the same Nom_semestre
I tried this query :
set #num_exam=0;
SELECT DISTINCT N_APPOGE, NOM, PRENOM, filiere,Nom_semestre,
(#num_exam:=#num_exam+1) as num_exam FROM etudiant,
module
WHERE
filiere in (SELECT filiere FROM etudiant WHERE N_APPOGE='1610065' )
And
Nom_semestre In
(SELECT Nom_semestre from module WHERE Nom_semestre='s1'
and NUM_module in (SELECT NUM_module from inscrit where N_APPOGE='1610065'))
ORDER by NOM;
but the result was not like I expected it shows two result of the same student with N_APPOGE='1610065' and multiple result for other student as well
It looks like DISTINCT in this case does not work what's the solution here ?

Answer 1

You have a join between etudiant and module, but in the WHERE clause there is nothing which specifies how these two tables are related. As such, the database is performing a cross join (each row in the first table is joined to each row in the second table). Apparently you need to get the table inscrit involved:
SELECT DISTINCT e.N_APPOGE,
e.NOM,
e.PRENOM,
e.filiere,
m.Nom_semestre,
(#num_exam:=#num_exam+1) as num_exam
FROM etudiant e
INNER JOIN inscrit i
ON i.N_Appoge = e.N_Appoge
INNER JOIN module m
ON m.NUM_Module = i.NUM_Module
WHERE e.filiere in (SELECT filiere
FROM etudiant
WHERE N_APPOGE='1610065') And
m.Nom_semestre In (SELECT Nom_semestre
from module
WHERE Nom_semestre='s1' and
NUM_module in (SELECT NUM_module
from inscrit
where N_APPOGE='1610065'))
ORDER by NOM
Hopefully that will help.