Function setPosition

src/jrd/optimizer/Optimizer.cpp:550–583

	}

	void setPosition(const SortNode* from_clause, SortNode* to_clause, const MapNode* map)
	{
		// Update the fields in a GROUP BY, DISTINCT, or ORDER BY clause to the same position
		// as another clause, possibly using a mapping between the streams.

		// Track the position in the from list with "to_swap", and find the corresponding
		// field in the from list with "to_ptr", then swap the two fields.  By the time
		// we get to the end of the from list, all fields in the to list will be reordered.

		auto to_swap = to_clause->expressions.begin();

		// We need to process no more than the number of nodes in the "from" clause

		const auto count = from_clause->expressions.getCount();
		fb_assert(count <= to_clause->expressions.getCount());

		auto from_ptr = from_clause->expressions.begin();
		for (const auto from_end = from_ptr + count; from_ptr != from_end; ++from_ptr)
		{
			NestConst<ValueExprNode>* to_ptr = to_clause->expressions.begin();
			for (const auto to_end = to_ptr + count; to_ptr != to_end; ++to_ptr)
			{
				if ((map && mapEqual(*to_ptr, *from_ptr, map)) ||
					(!map && fieldEqual(*to_ptr, *from_ptr)))
				{
					ValueExprNode* swap = *to_swap;
					*to_swap = *to_ptr;
					*to_ptr = swap;
				}
			}

			++to_swap;
		}
	}

} // namespace