ClickHouse/dbms/src/Interpreters/sortBlock.cpp

#include <Interpreters/sortBlock.h>

#include <Columns/ColumnString.h>
#include <Common/typeid_cast.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int BAD_COLLATION;
}


using ColumnsWithSortDescriptions = std::vector<std::pair<const IColumn *, SortColumnDescription>>;

static ColumnsWithSortDescriptions getColumnsWithSortDescription(const Block & block, const SortDescription & description)
{
    size_t size = description.size();
    ColumnsWithSortDescriptions res;
    res.reserve(size);

    for (size_t i = 0; i < size; ++i)
    {
        const IColumn * column = !description[i].column_name.empty()
            ? block.getByName(description[i].column_name).column.get()
            : block.safeGetByPosition(description[i].column_number).column.get();

        res.emplace_back(column, description[i]);
    }

    return res;
}


static inline bool needCollation(const IColumn * column, const SortColumnDescription & description)
{
    if (!description.collator)
        return false;

    if (!typeid_cast<const ColumnString *>(column))    /// TODO Nullable(String)
        throw Exception("Collations could be specified only for String columns.", ErrorCodes::BAD_COLLATION);

    return true;
}


struct PartialSortingLess
{
    const ColumnsWithSortDescriptions & columns;

    explicit PartialSortingLess(const ColumnsWithSortDescriptions & columns_) : columns(columns_) {}

    bool operator() (size_t a, size_t b) const
    {
        for (ColumnsWithSortDescriptions::const_iterator it = columns.begin(); it != columns.end(); ++it)
        {
            int res = it->second.direction * it->first->compareAt(a, b, *it->first, it->second.nulls_direction);
            if (res < 0)
                return true;
            else if (res > 0)
                return false;
        }
        return false;
    }
};

struct PartialSortingLessWithCollation
{
    const ColumnsWithSortDescriptions & columns;

    explicit PartialSortingLessWithCollation(const ColumnsWithSortDescriptions & columns_) : columns(columns_) {}

    bool operator() (size_t a, size_t b) const
    {
        for (ColumnsWithSortDescriptions::const_iterator it = columns.begin(); it != columns.end(); ++it)
        {
            int res;
            if (needCollation(it->first, it->second))
            {
                const ColumnString & column_string = typeid_cast<const ColumnString &>(*it->first);
                res = column_string.compareAtWithCollation(a, b, *it->first, *it->second.collator);
            }
            else
                res = it->first->compareAt(a, b, *it->first, it->second.nulls_direction);

            res *= it->second.direction;
            if (res < 0)
                return true;
            else if (res > 0)
                return false;
        }
        return false;
    }
};


void sortBlock(Block & block, const SortDescription & description, size_t limit)
{
    if (!block)
        return;

    /// If only one column to sort by
    if (description.size() == 1)
    {
        bool reverse = description[0].direction == -1;

        const IColumn * column = !description[0].column_name.empty()
            ? block.getByName(description[0].column_name).column.get()
            : block.safeGetByPosition(description[0].column_number).column.get();

        IColumn::Permutation perm;
        if (needCollation(column, description[0]))
        {
            const ColumnString & column_string = typeid_cast<const ColumnString &>(*column);
            column_string.getPermutationWithCollation(*description[0].collator, reverse, limit, perm);
        }
        else
            column->getPermutation(reverse, limit, description[0].nulls_direction, perm);

        size_t columns = block.columns();
        for (size_t i = 0; i < columns; ++i)
            block.getByPosition(i).column = block.getByPosition(i).column->permute(perm, limit);
    }
    else
    {
        size_t size = block.rows();
        IColumn::Permutation perm(size);
        for (size_t i = 0; i < size; ++i)
            perm[i] = i;

        if (limit >= size)
            limit = 0;

        bool need_collation = false;
        ColumnsWithSortDescriptions columns_with_sort_desc = getColumnsWithSortDescription(block, description);

        for (size_t i = 0, size = description.size(); i < size; ++i)
        {
            if (needCollation(columns_with_sort_desc[i].first, description[i]))
            {
                need_collation = true;
                break;
            }
        }

        if (need_collation)
        {
            PartialSortingLessWithCollation less_with_collation(columns_with_sort_desc);

            if (limit)
                std::partial_sort(perm.begin(), perm.begin() + limit, perm.end(), less_with_collation);
            else
                std::sort(perm.begin(), perm.end(), less_with_collation);
        }
        else
        {
            PartialSortingLess less(columns_with_sort_desc);

            if (limit)
                std::partial_sort(perm.begin(), perm.begin() + limit, perm.end(), less);
            else
                std::sort(perm.begin(), perm.end(), less);
        }

        size_t columns = block.columns();
        for (size_t i = 0; i < columns; ++i)
            block.getByPosition(i).column = block.getByPosition(i).column->permute(perm, limit);
    }
}


void stableGetPermutation(const Block & block, const SortDescription & description, IColumn::Permutation & out_permutation)
{
    if (!block)
        return;

    size_t size = block.rows();
    out_permutation.resize(size);
    for (size_t i = 0; i < size; ++i)
        out_permutation[i] = i;

    ColumnsWithSortDescriptions columns_with_sort_desc = getColumnsWithSortDescription(block, description);

    std::stable_sort(out_permutation.begin(), out_permutation.end(), PartialSortingLess(columns_with_sort_desc));
}


bool isAlreadySorted(const Block & block, const SortDescription & description)
{
    if (!block)
        return true;

    size_t rows = block.rows();

    ColumnsWithSortDescriptions columns_with_sort_desc = getColumnsWithSortDescription(block, description);

    PartialSortingLess less(columns_with_sort_desc);

    /** If the rows are not too few, then let's make a quick attempt to verify that the block is not sorted.
     * Constants - at random.
     */
    static constexpr size_t num_rows_to_try = 10;
    if (rows > num_rows_to_try * 5)
    {
        for (size_t i = 1; i < num_rows_to_try; ++i)
        {
            size_t prev_position = rows * (i - 1) / num_rows_to_try;
            size_t curr_position = rows * i / num_rows_to_try;

            if (less(curr_position, prev_position))
                return false;
        }
    }

    for (size_t i = 1; i < rows; ++i)
        if (less(i, i - 1))
            return false;

    return true;
}


void stableSortBlock(Block & block, const SortDescription & description)
{
    if (!block)
        return;

    IColumn::Permutation perm;
    stableGetPermutation(block, description, perm);

    size_t columns = block.columns();
    for (size_t i = 0; i < columns; ++i)
        block.safeGetByPosition(i).column = block.safeGetByPosition(i).column->permute(perm, 0);
}

}