Function mapEqual

src/jrd/optimizer/Optimizer.cpp:487–527

	}

	bool mapEqual(const ValueExprNode* field1, const ValueExprNode* field2, const MapNode* map)
	{
		// Test to see if two fields are equal, where the fields are in two different streams
		// possibly mapped to each other. Order of the input fields is important.
		const auto fieldNode1 = nodeAs<FieldNode>(field1);
		const auto fieldNode2 = nodeAs<FieldNode>(field2);

		if (!fieldNode1 || !fieldNode2)
			return false;

		// look through the mapping and see if we can find an equivalence.
		auto sourcePtr = map->sourceList.begin();
		auto targetPtr = map->targetList.begin();

		for (const auto sourceEnd = map->sourceList.end();
			 sourcePtr != sourceEnd;
			 ++sourcePtr, ++targetPtr)
		{
			const auto mapFrom = nodeAs<FieldNode>(*sourcePtr);
			const auto mapTo = nodeAs<FieldNode>(*targetPtr);

			if (!mapFrom || !mapTo)
				continue;

			if (fieldNode1->fieldStream != mapFrom->fieldStream ||
				fieldNode1->fieldId != mapFrom->fieldId)
			{
				continue;
			}

			if (fieldNode2->fieldStream != mapTo->fieldStream ||
				fieldNode2->fieldId != mapTo->fieldId)
			{
				continue;
			}

			return true;
		}

		return false;
	}

	void setDirection(SortNode* fromClause, SortNode* toClause)
	{