public function create_index(string $table, $column, bool $unique = false, $length = null): bool
	{
	  $column = (array)$column;
    if ( $length ){
      $length = (array)$length;
    }
    $name = bbn\str::encode_filename($table);
		if ( $table = $this->table_full_name($table, true) ){
      foreach ( $column as $i => $c ){
        if ( !bbn\str::check_name($c) ){
          $this->db->error("Illegal column $c");
        }
        $name .= '_'.$c;
        $column[$i] = $this->escape($column[$i]);
        if ( \is_int($length[$i]) && $length[$i] > 0 ){
          $column[$i] .= '('.$length[$i].')';
        }
      }
      $name = bbn\str::cut($name, 50);
			return (bool)$this->db->query('CREATE '.( $unique ? 'UNIQUE ' : '' )."INDEX `$name` ON $table ( ".
        implode(', ', $column).' )');
		}
		return false;
	}