Function updatePrewhereOutputsIfNeeded

src/Planner/PlannerJoinTree.cpp:520–582

}

void updatePrewhereOutputsIfNeeded(SelectQueryInfo & table_expression_query_info,
    const Names & column_names,
    const StorageSnapshotPtr & storage_snapshot)
{
    if (!table_expression_query_info.prewhere_info)
        return;

    auto & prewhere_actions = table_expression_query_info.prewhere_info->prewhere_actions;

    NameSet required_columns;
    if (column_names.size() == 1)
        required_columns.insert(column_names[0]);

    auto & table_expression_modifiers = table_expression_query_info.table_expression_modifiers;
    if (table_expression_modifiers)
    {
        if (table_expression_modifiers->hasSampleSizeRatio()
            || table_expression_query_info.planner_context->getQueryContext()->getSettingsRef()[Setting::parallel_replicas_count] > 1)
        {
            /// We evaluate sampling for Merge lazily so we need to get all the columns
            if (storage_snapshot->storage.getName() == "Merge")
            {
                const auto columns = storage_snapshot->metadata->getColumns().getAll();
                for (const auto & column : columns)
                    required_columns.insert(column.name);
            }
            else
            {
                auto columns_required_for_sampling = storage_snapshot->metadata->getColumnsRequiredForSampling();
                required_columns.insert(columns_required_for_sampling.begin(), columns_required_for_sampling.end());
            }
        }

        if (table_expression_modifiers->hasFinal())
        {
            auto columns_required_for_final = storage_snapshot->metadata->getColumnsRequiredForFinal();
            required_columns.insert(columns_required_for_final.begin(), columns_required_for_final.end());
        }
    }

    std::unordered_set<const ActionsDAG::Node *> required_output_nodes;

    for (const auto * input : prewhere_actions.getInputs())
    {
        if (required_columns.contains(input->result_name))
            required_output_nodes.insert(input);
    }

    if (required_output_nodes.empty())
        return;

    auto & prewhere_outputs = prewhere_actions.getOutputs();
    for (const auto & output : prewhere_outputs)
    {
        auto required_output_node_it = required_output_nodes.find(output);
        if (required_output_node_it == required_output_nodes.end())
            continue;