Method read

src/Storages/StorageWithCommonVirtualColumns.cpp:46–88

}

void StorageWithCommonVirtualColumns::read(
    QueryPlan & query_plan,
    const Names & column_names,
    const StorageSnapshotPtr & storage_snapshot,
    SelectQueryInfo & query_info,
    ContextPtr context,
    QueryProcessingStage::Enum processed_stage,
    size_t max_block_size,
    size_t num_streams)
{
    if (processed_stage > QueryProcessingStage::FetchColumns)
    {
        readImpl(query_plan, column_names, storage_snapshot, query_info, context, processed_stage, max_block_size, num_streams);
        return;
    }

    /// Proxy to underlying storage.
    auto filtered_columns = VirtualColumnUtils::filterVirtualColumns(column_names, storage_snapshot->metadata, VirtualsKind::Ephemeral, VirtualsMaterializationPlace::Plan);
    readImpl(query_plan, filtered_columns, storage_snapshot, query_info, context, processed_stage, max_block_size, num_streams);

    /// Materialize constant virtuals.
    if (query_plan.isInitialized())
    {
        if (std::ranges::contains(column_names, "_database") && !query_plan.getCurrentHeader()->has("_database"))
            materializeConstantColumn(query_plan, "_database", std::make_shared<DataTypeLowCardinality>(std::make_shared<DataTypeString>()), getStorageID().getDatabaseName());

        if (std::ranges::contains(column_names, "_table") && !query_plan.getCurrentHeader()->has("_table"))
        {
            std::string table_name = getStorageID().getTableName();
            if (query_info.table_expression)
                if (auto * table_node = query_info.table_expression->as<TableNode>())
                    if (table_node->isTemporaryTable())
                        table_name = table_node->getTemporaryTableName();

            materializeConstantColumn(query_plan, "_table", std::make_shared<DataTypeLowCardinality>(std::make_shared<DataTypeString>()), table_name);
        }
    }

    /// Match column_names sequence
    if (query_plan.isInitialized())
        if (filtered_columns != column_names)
            convertToHeader(query_plan, storage_snapshot->getSampleBlockForColumns(column_names), context);
}

void StorageWithCommonVirtualColumns::readImpl(
    QueryPlan & query_plan,