ClickHouse/dbms/src/Interpreters/sortBlock.cpp

#include <DB/Interpreters/sortBlock.h>


namespace DB
{

struct PartialSortingLess
{
	typedef std::vector<std::pair<const IColumn *, int> > Columns;
	Columns columns;

	PartialSortingLess(const Block & block, const SortDescription & description)
	{
		for (size_t i = 0, size = description.size(); i < size; ++i)
			columns.push_back(std::make_pair(
				!description[i].column_name.empty()
					? &*block.getByName(description[i].column_name).column
					: &*block.getByPosition(description[i].column_number).column,
				description[i].direction));
	}

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


void sortBlock(Block & block, const SortDescription & description)
{
	if (!block)
		return;
	
	/// Если столбец сортировки один
	if (description.size() == 1)
	{
		IColumn::Permutation perm = (!description[0].column_name.empty()
			? block.getByName(description[0].column_name).column
			: block.getByPosition(description[0].column_number).column)->getPermutation();

		if (description[0].direction == -1)
			for (size_t i = 0, size = perm.size(); i < size / 2; ++i)
				std::swap(perm[i], perm[size - 1 - i]);

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

		PartialSortingLess less(block, description);
		std::sort(perm.begin(), perm.end(), less);

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

}