Function getBlockSortPermutationImpl

src/Interpreters/sortBlock.cpp:108–183

}

void getBlockSortPermutationImpl(const Block & block, const SortDescription & description, IColumn::PermutationSortStability stability, UInt64 limit, IColumn::Permutation & permutation)
{
    if (!block)
        return;

    ColumnsWithSortDescriptions columns_with_sort_descriptions = getColumnsWithSortDescription(block, description);

    bool all_const = true;
    for (const auto & column : columns_with_sort_descriptions)
    {
        if (!column.column_const)
        {
            all_const = false;
            break;
        }
    }

    if (unlikely(all_const))
        return;

    /// If only one column to sort by
    if (columns_with_sort_descriptions.size() == 1)
    {
        auto & column_with_sort_description = columns_with_sort_descriptions[0];

        IColumn::PermutationSortDirection direction = column_with_sort_description.description.direction == -1 ? IColumn::PermutationSortDirection::Descending : IColumn::PermutationSortDirection::Ascending;
        int nan_direction_hint = column_with_sort_description.description.nulls_direction;
        const auto & column = column_with_sort_description.column;

        if (isCollationRequired(column_with_sort_description.description))
            column->getPermutationWithCollation(
                *column_with_sort_description.description.collator, direction, stability, limit, nan_direction_hint, permutation);
        else
            column->getPermutation(direction, stability, limit, nan_direction_hint, permutation);
    }
    else
    {
        size_t size = block.rows();
        permutation.resize(size);
        for (size_t i = 0; i < size; ++i)
            permutation[i] = i;

        if (limit >= size)
            limit = 0;

        EqualRanges ranges;
        ranges.emplace_back(0, permutation.size());

        for (const auto & column_with_sort_description : columns_with_sort_descriptions)
        {
            while (!ranges.empty() && limit && limit <= ranges.back().first)
                ranges.pop_back();

            if (ranges.empty())
                break;

            if (column_with_sort_description.column_const)
                continue;