Method buildSelectExpression

src/Analyzer/QueryTreeBuilder.cpp:262–562

}

QueryTreeNodePtr QueryTreeBuilder::buildSelectExpression(
    const ASTPtr & select_query,
    bool is_subquery,
    const CommonTableExpressionData & cte_data,
    const ASTPtr & aliases,
    const ContextPtr & context) const
{
    const auto & select_query_typed = select_query->as<ASTSelectQuery &>();

    auto updated_context = Context::createCopy(context);
    auto select_settings = select_query_typed.settings();
    SettingsChanges settings_changes;

    /// We are going to remove settings LIMIT and OFFSET and
    /// further replace them with corresponding expression nodes
    UInt64 limit = 0;
    UInt64 offset = 0;

    /// Remove global settings limit and offset
    if (const auto & settings_ref = updated_context->getSettingsRef(); settings_ref[Setting::limit] || settings_ref[Setting::offset])
    {
        Settings settings = updated_context->getSettingsCopy();
        limit = settings[Setting::limit];
        offset = settings[Setting::offset];
        settings[Setting::limit] = 0;
        settings[Setting::offset] = 0;
        updated_context->setSettings(settings);
    }

    if (select_settings)
    {
        auto & set_query = select_settings->as<ASTSetQuery &>();

        /// Remove expression settings limit and offset
        if (auto * limit_field = set_query.changes.tryGet("limit"))
        {
            limit = limit_field->safeGet<UInt64>();
            set_query.changes.removeSetting("limit");
        }
        if (auto * offset_field = set_query.changes.tryGet("offset"))
        {
            offset = offset_field->safeGet<UInt64>();
            set_query.changes.removeSetting("offset");
        }

        if (!set_query.changes.empty())
        {
            updated_context->applySettingsChanges(set_query.changes);
            settings_changes = set_query.changes;
        }
    }

    const auto enable_order_by_all = updated_context->getSettingsRef()[Setting::enable_order_by_all];

    auto current_query_tree = std::make_shared<QueryNode>(std::move(updated_context), std::move(settings_changes));

    current_query_tree->setIsSubquery(is_subquery);
    current_query_tree->setIsCTE(!cte_data.cte_name.empty());