/**
  * Get field object for sql
  * @param Field $field
  * @return string
  */
 protected function buildFieldForSql(Field $field, $withAlias = true)
 {
     $result = $this->alias . "." . $field->getDbName();
     if ($withAlias) {
         $result .= " AS " . $this->getFieldAliasForSql($field);
     }
     return $result;
 }