Method explainMetaData

src/Interpreters/InterpreterExplainQuery.cpp:792–950

}

BlockInputStreamPtr InterpreterExplainQuery::explainMetaData()
{
    const auto & explain = query->as<ASTExplainQuery &>();
    auto context = Context::createCopy(getContext());
    auto query_ptr = explain.getExplainedQuery();
    auto contxt = getContext();
    auto metadata_settings = checkAndGetSettings<QueryMetadataSettings>(explain.getSettings());
    AnalysisPtr analysis;
    QueryPlanPtr query_plan;

    if (metadata_settings.lineage || metadata_settings.lineage_use_optimizer)
    {
        try
        {
            InterpreterSelectQueryUseOptimizer interpreter(query_ptr, contxt, SelectQueryOptions());
            interpreter.buildQueryPlan(query_plan, analysis, !metadata_settings.lineage_use_optimizer);
            query_ptr = interpreter.getQuery();
        }
        catch (...)
        {
            tryLogWarningCurrentException(&Poco::Logger::get("InterpreterExplainQuery::explainMetaData"), "build plan failed.");
        }
    }

    if (!analysis)
    {
        query_ptr = QueryRewriter().rewrite(query_ptr, contxt);
        analysis = QueryAnalyzer::analyze(query_ptr, contxt);
    }

    if (metadata_settings.format_json)
    {
        String res = PlanPrinter::jsonMetaData(query_ptr, analysis, contxt, query_plan, metadata_settings);
        Block sample_block = getSampleBlock();
        MutableColumns res_columns = sample_block.cloneEmptyColumns();
        fillColumn(*res_columns[0], res);
        return std::make_shared<OneBlockInputStream>(sample_block.cloneWithColumns(std::move(res_columns)));
    }


    // get used tables, databases, columns_list
    auto column_tables = ColumnArray::create(ColumnString::create());
    auto column_databases = ColumnArray::create(ColumnString::create());
    auto column_columns_list = ColumnArray::create(ColumnString::create());

    auto column_lists_off = ColumnUInt64::create();
    auto & columns_list_offset_data = column_lists_off->getData();

    Array tables_array;
    Array databases_array;
    size_t array_off_size = 0;

    const auto & used_columns_map = analysis->getUsedColumns();
    for (const auto & [table_ast, storage_analysis] : analysis->getStorages())
    {
        Array columns_array;
        tables_array.push_back(storage_analysis.table);
        databases_array.push_back(storage_analysis.database);