code: protected function buildCol()/*# : array */
      {
          $result = [];
  
          // all cols
          if (empty($this->clause_column)) {
              $result[] = '*';
  
          // specific cols
          } else {
              foreach ($this->clause_column as $as => $col) {
                  // col alias
                  $alias = is_int($as) ? '' : (' AS ' . $this->quoteSpace($as));
  
                  // rawMode ?
                  $field = $col[0] ? $col[1] : $this->quote($col[1]);
  
                  // function ?
                  if (isset($col[2])) {
                      $field = sprintf($col[2], $field);
                  }
                  $result[] = $field . $alias;
              }
          }
          return $result;
      }
docs: Build columns
  
  @return array
  @access protected