Load table from a choice list in PHP

Question

I have a combobox with data base values

<select name="name_user">
      <?php
           $req00 = $bdd->prepare('SELECT * FROM user');
           $req00->execute();
           while($donnees00 = $req00->fetch())
           {
               ?>
                   <option><?php echo $donnees00['name'];?></option>                                    
               <?php
           }
      ?>
</select>

I have to fill the table from the database but in the WHERE clause I have to specify the value in the choice list.

Can you help me please? I don't know how to do that. An example would be great.