public function sumSubtable(DataTable $subTable)
    {
        if ($this->isSubtableLoaded) {
            $thisSubTable = $this->getSubtable();
        } else {
            $this->warnIfSubtableAlreadyExists();

            $thisSubTable = new DataTable();
            $this->setSubtable($thisSubTable);
        }
        $columnOps = $subTable->getMetadata(DataTable::COLUMN_AGGREGATION_OPS_METADATA_NAME);
        $thisSubTable->setMetadata(DataTable::COLUMN_AGGREGATION_OPS_METADATA_NAME, $columnOps);
        $thisSubTable->addDataTable($subTable);
    }