title: Adding LEFT JOIN add results or modify them
body: <p>My tables are designed like that: cours>modules>sections>parts I mean there's courses, inside courses there's modules, inside modules there's sections...</p>
  
  <p>This is my actual query:</p>
  
  <pre><code>SELECT PG.idpage,PG.type
                  FROM pages PG
                  JOIN parts P            ON P.idpart=PG.idpart
                  JOIN sections S         ON S.idsection=P.idsection
                  JOIN modules M          ON M.idmodule=S.idmodule
                  JOIN coursuser CU       ON CU.idcours=M.idcours     
                  WHERE PG.idpart='15' AND CU.iduser='1'
                  ORDER BY idpage;
  </code></pre>
  
  <p>What I'm trying:</p>
  
  <pre><code>SELECT PG.idpage,PG.type,R.time
                  FROM pages PG
                  JOIN parts P            ON P.idpart=PG.idpart
                  JOIN sections S         ON S.idsection=P.idsection
                  JOIN modules M          ON M.idmodule=S.idmodule
                  JOIN coursuser CU       ON CU.idcours=M.idcours     
                  LEFT JOIN reads R   ON R.idpage=PG.idpage   
                  WHERE PG.idpart='15' AND CU.iduser='1'
                  ORDER BY idpage;
  </code></pre>
  
  <p>I expected to have the same results with just the columns of reads added, but this is not the case, why ?</p>