public function delete_relation($site_1, $site_2 = 0)
{
$query = "DELETE FROM {$this->table}";
if (!$site_2) {
$query .= " WHERE site_1 = %d OR site_2 = %d";
$args = [$site_1, $site_1];
} else {
$query .= " WHERE (site_1 = %d AND site_2 = %d) OR (site_1 = %d AND site_2 = %d)";
$args = [$site_1, $site_2, $site_2, $site_1];
}
$query = $this->db->prepare($query, $args);
return (int) $this->db->query($query);
}