Method executeImpl

src/Interpreters/InterpreterSelectQuery.cpp:1185–1698

void InterpreterSelectQuery::executeImpl(QueryPlan & query_plan, const BlockInputStreamPtr & prepared_input, std::optional<Pipe> prepared_pipe)
{
    /** Streams of data. When the query is executed in parallel, we have several data streams.
     *  If there is no GROUP BY, then perform all operations before ORDER BY and LIMIT in parallel, then
     *  if there is an ORDER BY, then glue the streams using ResizeProcessor, and then MergeSorting transforms,
     *  if not, then glue it using ResizeProcessor,
     *  then apply LIMIT.
     *  If there is GROUP BY, then we will perform all operations up to GROUP BY, inclusive, in parallel;
     *  a parallel GROUP BY will glue streams into one,
     *  then perform the remaining operations with one resulting stream.
     */

    /// Now we will compose block streams that perform the necessary actions.
    auto & query = getSelectQuery();

    const Settings & settings = context->getSettingsRef();
    auto & expressions = analysis_result;
    auto & subqueries_for_sets = query_analyzer->getSubqueriesForSets();
    bool intermediate_stage = false;
    bool to_aggregation_stage = false;
    bool from_aggregation_stage = false;

    /// Do I need to aggregate in a separate row rows that have not passed max_rows_to_group_by.
    bool aggregate_overflow_row =
        expressions.need_aggregate &&
        query.group_by_with_totals &&
        settings.max_rows_to_group_by &&
        settings.group_by_overflow_mode == OverflowMode::ANY &&
        settings.totals_mode != TotalsMode::AFTER_HAVING_EXCLUSIVE;

    /// Do I need to immediately finalize the aggregate functions after the aggregation?
    bool aggregate_final =
        expressions.need_aggregate &&
        options.to_stage > QueryProcessingStage::WithMergeableState &&
        !query.group_by_with_totals && !query.group_by_with_rollup && !query.group_by_with_cube;

    bool use_grouping_set_key = expressions.use_grouping_set_key;

    if (query.group_by_with_grouping_sets && query.group_by_with_totals)
       throw Exception("WITH TOTALS and GROUPING SETS are not supported together", ErrorCodes::NOT_IMPLEMENTED);

    if (query_info.projection && query_info.projection->desc->type == ProjectionDescription::Type::Aggregate)
    {
        query_info.projection->aggregate_overflow_row = aggregate_overflow_row;
        query_info.projection->aggregate_final = aggregate_final;
    }

    if (options.only_analyze)
    {
        auto read_nothing = std::make_unique<ReadNothingStep>(source_header);
        query_plan.addStep(std::move(read_nothing));

        if (expressions.filter_info)
        {
            auto row_level_security_step = std::make_unique<FilterStep>(
                query_plan.getCurrentDataStream(),
                expressions.filter_info->actions,
                expressions.filter_info->column_name,