ClickHouse/src/Interpreters/InterpreterSelectWithUnionQuery.cpp

#include <Interpreters/InterpreterSelectWithUnionQuery.h>
#include <Interpreters/InterpreterSelectQuery.h>
#include <Interpreters/Context.h>
#include <Parsers/ASTSelectWithUnionQuery.h>
#include <Parsers/ASTSelectQuery.h>
#include <Columns/getLeastSuperColumn.h>
#include <Common/typeid_cast.h>
#include <Parsers/queryToString.h>

#include <Processors/Sources/NullSource.h>
#include <Processors/QueryPipeline.h>
#include <Processors/Pipe.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int LOGICAL_ERROR;
    extern const int UNION_ALL_RESULT_STRUCTURES_MISMATCH;
}


InterpreterSelectWithUnionQuery::InterpreterSelectWithUnionQuery(
    const ASTPtr & query_ptr_,
    const Context & context_,
    const SelectQueryOptions & options_,
    const Names & required_result_column_names)
    : options(options_),
    query_ptr(query_ptr_),
    context(std::make_shared<Context>(context_)),
    max_streams(context->getSettingsRef().max_threads)
{
    const auto & ast = query_ptr->as<ASTSelectWithUnionQuery &>();

    size_t num_selects = ast.list_of_selects->children.size();

    if (!num_selects)
        throw Exception("Logical error: no children in ASTSelectWithUnionQuery", ErrorCodes::LOGICAL_ERROR);

    /// Initialize interpreters for each SELECT query.
    /// Note that we pass 'required_result_column_names' to first SELECT.
    /// And for the rest, we pass names at the corresponding positions of 'required_result_column_names' in the result of first SELECT,
    ///  because names could be different.

    nested_interpreters.reserve(num_selects);

    std::vector<Names> required_result_column_names_for_other_selects(num_selects);
    if (!required_result_column_names.empty() && num_selects > 1)
    {
        /// Result header if there are no filtering by 'required_result_column_names'.
        /// We use it to determine positions of 'required_result_column_names' in SELECT clause.

        Block full_result_header = InterpreterSelectQuery(
            ast.list_of_selects->children.at(0), *context, options.copy().analyze().noModify()).getSampleBlock();

        std::vector<size_t> positions_of_required_result_columns(required_result_column_names.size());
        for (size_t required_result_num = 0, size = required_result_column_names.size(); required_result_num < size; ++required_result_num)
            positions_of_required_result_columns[required_result_num] = full_result_header.getPositionByName(required_result_column_names[required_result_num]);

        for (size_t query_num = 1; query_num < num_selects; ++query_num)
        {
            Block full_result_header_for_current_select = InterpreterSelectQuery(
                ast.list_of_selects->children.at(query_num), *context, options.copy().analyze().noModify()).getSampleBlock();

            if (full_result_header_for_current_select.columns() != full_result_header.columns())
                throw Exception("Different number of columns in UNION ALL elements:\n"
                    + full_result_header.dumpNames()
                    + "\nand\n"
                    + full_result_header_for_current_select.dumpNames() + "\n",
                    ErrorCodes::UNION_ALL_RESULT_STRUCTURES_MISMATCH);

            required_result_column_names_for_other_selects[query_num].reserve(required_result_column_names.size());
            for (const auto & pos : positions_of_required_result_columns)
                required_result_column_names_for_other_selects[query_num].push_back(full_result_header_for_current_select.getByPosition(pos).name);
        }
    }

    for (size_t query_num = 0; query_num < num_selects; ++query_num)
    {
        const Names & current_required_result_column_names
            = query_num == 0 ? required_result_column_names : required_result_column_names_for_other_selects[query_num];

        nested_interpreters.emplace_back(std::make_unique<InterpreterSelectQuery>(
            ast.list_of_selects->children.at(query_num),
            *context,
            options,
            current_required_result_column_names));
    }

    /// Determine structure of the result.

    if (num_selects == 1)
    {
        result_header = nested_interpreters.front()->getSampleBlock();
    }
    else
    {
        Blocks headers(num_selects);
        for (size_t query_num = 0; query_num < num_selects; ++query_num)
            headers[query_num] = nested_interpreters[query_num]->getSampleBlock();

        result_header = getCommonHeaderForUnion(headers);
    }

    /// InterpreterSelectWithUnionQuery ignores limits if all nested interpreters ignore limits.
    bool all_nested_ignore_limits = true;
    bool all_nested_ignore_quota = true;
    for (auto & interpreter : nested_interpreters)
    {
        if (!interpreter->ignoreLimits())
            all_nested_ignore_limits = false;
        if (!interpreter->ignoreQuota())
            all_nested_ignore_quota = false;
    }
    options.ignore_limits |= all_nested_ignore_limits;
    options.ignore_quota |= all_nested_ignore_quota;
}


Block InterpreterSelectWithUnionQuery::getCommonHeaderForUnion(const Blocks & headers)
{
    size_t num_selects = headers.size();
    Block common_header = headers.front();
    size_t num_columns = common_header.columns();

    for (size_t query_num = 1; query_num < num_selects; ++query_num)
    {
        if (headers[query_num].columns() != num_columns)
            throw Exception("Different number of columns in UNION ALL elements:\n"
                            + common_header.dumpNames()
                            + "\nand\n"
                            + headers[query_num].dumpNames() + "\n",
                            ErrorCodes::UNION_ALL_RESULT_STRUCTURES_MISMATCH);
    }

    std::vector<const ColumnWithTypeAndName *> columns(num_selects);

    for (size_t column_num = 0; column_num < num_columns; ++column_num)
    {
        for (size_t i = 0; i < num_selects; ++i)
            columns[i] = &headers[i].getByPosition(column_num);

        ColumnWithTypeAndName & result_elem = common_header.getByPosition(column_num);
        result_elem = getLeastSuperColumn(columns);
    }

    return common_header;
}


InterpreterSelectWithUnionQuery::~InterpreterSelectWithUnionQuery() = default;


Block InterpreterSelectWithUnionQuery::getSampleBlock()
{
    return result_header;
}

Block InterpreterSelectWithUnionQuery::getSampleBlock(
    const ASTPtr & query_ptr,
    const Context & context)
{
    auto & cache = context.getSampleBlockCache();
    /// Using query string because query_ptr changes for every internal SELECT
    auto key = queryToString(query_ptr);
    if (cache.find(key) != cache.end())
    {
        return cache[key];
    }

    return cache[key] = InterpreterSelectWithUnionQuery(query_ptr, context, SelectQueryOptions().analyze()).getSampleBlock();
}


BlockIO InterpreterSelectWithUnionQuery::execute()
{
    BlockIO res;
    QueryPipeline & main_pipeline = res.pipeline;
    std::vector<QueryPipeline> pipelines;
    bool has_main_pipeline = false;

    Blocks headers;
    headers.reserve(nested_interpreters.size());

    for (auto & interpreter : nested_interpreters)
    {
        if (!has_main_pipeline)
        {
            has_main_pipeline = true;
            main_pipeline = interpreter->execute().pipeline;
            headers.emplace_back(main_pipeline.getHeader());
        }
        else
        {
            pipelines.emplace_back(interpreter->execute().pipeline);
            headers.emplace_back(pipelines.back().getHeader());
        }
    }

    if (!has_main_pipeline)
        main_pipeline.init(Pipe(std::make_shared<NullSource>(getSampleBlock())));

    if (!pipelines.empty())
    {
        auto common_header = getCommonHeaderForUnion(headers);
        main_pipeline.unitePipelines(std::move(pipelines), common_header);

        // nested queries can force 1 thread (due to simplicity)
        // but in case of union this cannot be done.
        UInt64 max_threads = context->getSettingsRef().max_threads;
        main_pipeline.setMaxThreads(std::min<UInt64>(nested_interpreters.size(), max_threads));
    }

    main_pipeline.addInterpreterContext(context);

    return res;
}


void InterpreterSelectWithUnionQuery::ignoreWithTotals()
{
    for (auto & interpreter : nested_interpreters)
        interpreter->ignoreWithTotals();
}

}