$col1 = 1;
$res = $this->db->prepare('SELECT COUNT(`column1`) FROM table WHERE column1 = ?);
$res->bindParam(1, $col1);
$res->execute();
$column1 = $res->fetchColumn();
или надо писать еще раз запрос
$col2 = 1;
$res = $this->db->prepare('SELECT COUNT(`column2`) FROM table WHERE column2 = ?);
$res->bindParam(1, $col2);
$res->execute();
$column2 = $res->fetchColumn();