Checkbox keeps showing up on filter

<label>Filter by therapist clients</label>
      <?php
$sql = <<< EOT
          SELECT tbl_client.client_id, tbl_client.client_name
        FROM tbl_client
        JOIN tbl_therapist_client
        ON tbl_therapist_client.client_id=tbl_client.client_id
         JOIN tbl_session
        ON tbl_session.client_id=tbl_client.client_id
         WHERE tbl_therapist_client.therapist_id = $therapist_id
           AND tbl_session.session_status = "Paid"
         GROUP BY tbl_client.client_id
        ORDER BY tbl_client.client_name ASC;
EOT;
        $results = $db->query($sql);
        echo "<select name='myClients'>";
      echo "<option value='0'>Show All</option>";
      while ($row = $results->fetch(PDO::FETCH_OBJ)) {
         printf("<option value='%s'>%s</option>", $row->client_id, $row->client_name);
      }
         echo "</select>";   
   ?>