title: Join on nullable column
body: <p><a href="https://i.stack.imgur.com/gbFc7.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gbFc7.jpg" alt="enter image description here"></a>My query is like this:</p>
  
  <pre><code>SELECT * FROM inscription i
  INNER JOIN employeGroupe ge
  ON i.IDGroupe=ge.IDGroupe
  INNER JOIN Employe e
  ON e.IDEmploye=ge.IDEmploye
  INNER JOIN cOURS BC
  on bc.IDCours=i.IDCours
  </code></pre>
  
  <p>I have 4 tables as follows:</p>
  
  <pre><code>Inscription
  EmployeeGroupe
  Employee
  Cours
  Column IDGroupe in table Inscription relates to table EmployeeGroupe
  Column IDEmploe in table EmployeeGroupe relates to table Employee
  Column IDCours in table Inscription relates to table Cours
  </code></pre>
  
  <p>My problem is that I want to display the names of related employes to cours. We can find the cours into inscription table. Not that INscription.IDGroupe for some cours is null then I am not able to bring up the EmployeGroupe related which go up to EmployeID in Employe table.</p>
  
  <p>My query is like this:</p>
  
  <pre><code>SELECT * FROM inscription i
  INNER JOIN employeGroupe ge
  ON i.IDGroupe=ge.IDGroupe
  INNER JOIN Employe e
  ON e.IDEmploye=ge.IDEmploye
  INNER JOIN cOURS BC
  on bc.IDCours=i.IDCours
  </code></pre>