Method getSampleBlock

src/Interpreters/InterpreterSelectWithUnionQuery.cpp:276–305

InterpreterSelectWithUnionQuery::~InterpreterSelectWithUnionQuery() = default;

SharedHeader InterpreterSelectWithUnionQuery::getSampleBlock(const ASTPtr & query_ptr_, ContextPtr context_, bool is_subquery, bool is_create_parameterized_view)
{
    if (!context_->hasQueryContext())
    {
        SelectQueryOptions options;
        if (is_subquery)
            options = options.subquery();
        if (is_create_parameterized_view)
            options = options.createParameterizedView();
        return InterpreterSelectWithUnionQuery(query_ptr_, context_, std::move(options.analyze())).getSampleBlock();
    }

    /// Using query string because query_ptr changes for every internal SELECT
    auto key = query_ptr_->formatWithSecretsOneLine();
    {
        auto [cache, lock] = context_->getSampleBlockCache();
        if (cache->contains(key))
            return cache->at(key);
    }

    SelectQueryOptions options;
    if (is_subquery)
        options = options.subquery();
    if (is_create_parameterized_view)
        options = options.createParameterizedView();

    auto sample_block = InterpreterSelectWithUnionQuery(query_ptr_, context_, std::move(options.analyze())).getSampleBlock();
    auto [cache, lock] = context_->getSampleBlockCache();
    return (*cache)[key] = sample_block;
}


void InterpreterSelectWithUnionQuery::buildQueryPlan(QueryPlan & query_plan)