NilPortugues\Sql\QueryBuilder\Manipulation\Select::getColumnValues PHP Method

    public function getColumnValues()
    {
        return $this->columnQuery->getColumnValues();
    }

 /**
  * @param Select $select
  *
  * @return array
  */
 public function writeValueAsColumns(Select $select)
 {
     $valueAsColumns = $select->getColumnValues();
     $newColumns = [];
     if (!empty($valueAsColumns)) {
         foreach ($valueAsColumns as $alias => $value) {
             $value = $this->writer->writePlaceholderValue($value);
             $newValueColumn = array($alias => $value);
             $newColumns[] = SyntaxFactory::createColumn($newValueColumn, null);
         }
     }
     return $newColumns;
 }