Method initLoop

src/Processors/QueryPlan/ReadFromLoopStep.cpp:119–166

    String getName() const override { return "Loop"; }

    void initLoop()
    {
        if (loop)
            return;

        QueryPlan plan;

        if (DatabaseCatalog::instance().isTableExist(inner_storage->getStorageID(), context))
        {
            inner_context = Context::createCopy(context);
            const auto & storage_id = inner_storage->getStorageID();
            buildSelectQueryPlan(
                plan, column_names, query_info, inner_context,
                storage_id.database_name, storage_id.table_name);
        }
        else if (inner_table_function_ast)
        {
            inner_context = Context::createCopy(context);
            buildSelectQueryPlan(
                plan, column_names, query_info, inner_context,
                {}, {}, inner_table_function_ast);
        }
        else
        {
            const auto metadata_snapshot = inner_storage->getInMemoryMetadataPtr(context, false);
            auto inner_storage_snapshot = inner_storage->getStorageSnapshot(metadata_snapshot, context);
            inner_storage->read(
                    plan,
                    column_names,
                    inner_storage_snapshot,
                    query_info,
                    context,
                    processed_stage,
                    max_block_size,
                    num_streams);
        }

        if (plan.isInitialized())
        {
            auto builder = plan.buildQueryPipeline(QueryPlanOptimizationSettings(context), BuildQueryPipelineSettings(context));
            QueryPlanResourceHolder resources;
            auto pipe = QueryPipelineBuilder::getPipe(std::move(*builder), resources);
            query_pipeline = QueryPipeline(std::move(pipe));
            query_pipeline.addResources(std::move(resources));
            executor = std::make_unique<PullingPipelineExecutor>(query_pipeline);
        }
        loop = true;
    }

    Chunk generate() override
    {