title: Filter Posts depending ID of categorie with PHP
body: <p>I have a small task where I have a mysql table "blog".It contains a column "ID_CAT". Each field of ID_CAT contains diiferent values of category for one single article like "22,44,33,55" .
  I want to filter the posts of blog depending on the category choosing . i pass the ID_CAT choosing into URL and GET methode in the included page like that</p>
  
  <pre><code>&lt;a class="rotated_link" href="?cat='.$categorie-&gt;getIDCategorie().'"&gt;'.$categorie-&gt;getNomCategorie().'&lt;/a&gt;
  </code></pre>
  
  <p>then the page included like that</p>
  
  <pre><code>$id_categorie = $_GET["cat"];
  if (isset($id_categorie)) {
  
    foreach(Article::getAllArticlebycategorie($id_categorie) as $all){
                  $article= new Article($all-&gt;ID_BLOG);
                  $img=Image::getImageByArticle($article-&gt;getIDarticle());
                  $tblCat=explode(',',$article-&gt;getIDCategorie());
                      echo '&lt;li class="li_blog_post"&gt;';
                              echo'&lt;img class="img_post_mini" src="img/file/'.$img.'" style="width:100%; height:150px; border:1PX solid #9D9D9D;" /&gt;';
                              echo'&lt;span class="post_title0"&gt;'.$article-&gt;getTitlearticle().'&lt;/span&gt;';
                              echo'&lt;span class="tag_post"&gt;&lt;img src="img/tag.png" style="width:16px; height:16px;"/&gt;';
                      foreach($tblCat as $catt){
                          $categoriea = new Categorie($catt);
  
                      echo '&lt;a class="tag_lable" href=""&gt;'.$categoriea-&gt;getNomCategorie().'&lt;/a&gt; &lt;/span&gt;';
                      }
                      echo'&lt;p class="post_prev"&gt;'.substr($article-&gt;getArticle(), 0, 410).'&amp;nbsp;...&lt;/p&gt;';
                      echo'&lt;span class="date"&gt;le&amp;nbsp;'.$article-&gt;getDatearticle().'&lt;/span&gt; &lt;span class="view_more"&gt;&lt;a class="test" href="?article='.$article-&gt;getIDarticle().'"&gt;voire les détails&lt;/a&gt;&lt;/span&gt;';
                     echo '&lt;/li&gt;';
                  }  
  
  }
  </code></pre>
  
  <p>the probleme is when i choose for example ID_CAT=4 , the function getAllArticlebycategorie returne the posts only if the number 4 is the first value in column ID_CAT (4,33,50)-> selected (3,4,10)-> not selected .
  the function :</p>
  
  <pre><code>public static function getAllArticlebycategorie($id_categorie){
      global $db;
      $req = $db-&gt;prepare('SELECT * FROM blog WHERE ID_CAT='.$id_categorie);
      $req-&gt;execute();
      return $req-&gt;fetchAll(PDO::FETCH_OBJ);
  }
  </code></pre>