code: private function addColumn($column, &$columns)
      {
          if (isset($columns[$column])) {
              return $columns[$column];
          }
          $name = 'c' . preg_replace("/[^a-z]+/i", "", $column) . count($columns);
  
          return $columns[$column] = $name;
      }
docs: Adds a column to the list of columns to retrieve and creates an alias
  @param string $column the column name to add
  @param array $columns list of columns given by reference
  @return string the alias generated for the column name