Method executeImpl

src/Interpreters/InterpreterExplainQuery.cpp:626–926

}

QueryPipeline InterpreterExplainQuery::executeImpl()
{
    const auto & ast = query->as<const ASTExplainQuery &>();

    Block sample_block = getSampleBlock(ast.getKind());
    MutableColumns res_columns = sample_block.cloneEmptyColumns();

    WriteBufferFromOwnString buf;
    bool single_line = false;
    bool insert_buf = true;

    ContextPtr query_context = getContext();

    options.setExplain();
    options.max_step_description_length = query_context->getSettingsRef()[Setting::query_plan_max_step_description_length];

    /// https://github.com/ClickHouse/ClickHouse/issues/88467
    /// EXPLAIN is to get a good picture of how the query will execute after *static* planning.
    /// Hence disable any optimizations that stagger the planning or introduce variablility due to caches.
    auto explain_query_context = Context::createCopy(query_context);
    explain_query_context->setSetting("use_skip_indexes_on_data_read", false);
    explain_query_context->setSetting("use_query_condition_cache", false);
    InterpreterSetQuery::applySettingsFromQuery(query, explain_query_context);
    query_context = std::move(explain_query_context);

    switch (ast.getKind())
    {
        case ASTExplainQuery::ParsedAST:
        {
            auto settings = checkAndGetSettings<QueryASTSettings>(ast.getSettings());
            if (settings.optimize)
            {
                ExplainAnalyzedSyntaxVisitor::Data data(query_context);
                ExplainAnalyzedSyntaxVisitor(data).visit(query);
            }

            if (settings.graph)
                dumpASTInDotFormat(*ast.getExplainedQuery(), buf);
            else
                dumpAST(*ast.getExplainedQuery(), buf);
            break;
        }
        case ASTExplainQuery::AnalyzedSyntax:
        {
            auto settings = checkAndGetSettings<QuerySyntaxSettings>(ast.getSettings());

            /// Inline any parameterized view calls with their parameter-substituted inner queries,
            /// so EXPLAIN SYNTAX shows what the view actually expands to.
            ExpandParameterizedViewsMatcher::Data expand_views_data(query_context);
            ExpandParameterizedViewsVisitor(expand_views_data).visit(query);

            if (query_context->getSettingsRef()[Setting::allow_experimental_analyzer])
            {
                bool explain_ok = explainQueryTree(ast.getExplainedQuery(), query_context, QueryTreeSettings{
                    .run_passes = settings.run_query_tree_passes,
                    .dump_tree = false,
                    .dump_passes = false,
                    .dump_ast = true,