如何在变量PHP中执行PDO

while($row =$result->fetch())
 {
       $output .= ' 
  <tr>  
       <td>' . $row["ID_personne"] . '</td> 
       <td>' . $row["Nom"] . '</td>  
       <td>' . $row["Prenom"] . '</td>  
       <td>' . $row["Telephone"] . '</td>  
       <td>' . $row["Mail"] . '</td>  
       <td>' . $row["Categorie"] . '</td>  
       <td>' . $row["Type"] . '</td>
            '.$q2 = $db->prepare("SELECT * FROM entretiens WHERE ID_entretien=:id");
            $q2->bindValue(":id",$row["Entretien"]);
            $q2->execute();
            $entretien=$q2->fetch().'

       <td>'.$entretien["Date"].'</td>  
       <td width=250>
                <a class="btn btn-primary" href="update_personnes.php?ID_personne='.$row["ID_personne"].'"><span class="glyphicon glyphicon-pencil"></span> Modifier</a>

                <a class="btn btn-danger" href="delete_personnes.php?ID_personne='.$row["ID_personne"].'"><span class="glyphicon glyphicon-remove"></span> Supprimer</a>
        </td>  
  </tr>';
  }
 $output .= '</table>';
 echo $output;

I have always an Error: ( ! ) Catchable fatal error: Object of class PDOStatement could not be converted to string in C:.......... on line 61('.$q2 = $db->prepare("SELECT * FROM entretiens WHERE ID_entretien=:id"); $row["Entretien"] it's a foreign key

There was some syntax error in your code as $q2 is being concat with html string. Improved code should be:

while ($row = $result->fetch()) {
    $output .= ' 
  <tr>  
       <td>' . $row["ID_personne"] . '</td> 
       <td>' . $row["Nom"] . '</td>  
       <td>' . $row["Prenom"] . '</td>  
       <td>' . $row["Telephone"] . '</td>  
       <td>' . $row["Mail"] . '</td>  
       <td>' . $row["Categorie"] . '</td>
       <td>' . $row["Type"] . '</td>';
    $q2 = $db->prepare("SELECT * FROM entretiens WHERE ID_entretien=:id");
    $q2->bindValue(":id", $row["Entretien"]);
    $q2->execute();
    $entretien = $q2->fetch();

    $output .= '<td>' . $entretien["Date"] . '</td>  
       <td width=250>
                <a class="btn btn-primary" href="update_personnes.php?ID_personne=' . $row["ID_personne"] . '"><span class="glyphicon glyphicon-pencil"></span> Modifier</a>

                <a class="btn btn-danger" href="delete_personnes.php?ID_personne=' . $row["ID_personne"] . '"><span class="glyphicon glyphicon-remove"></span> Supprimer</a>
        </td>  
  </tr>';
}
$output .= '</table>';
echo $output;