Method checkSorts

src/jrd/optimizer/Optimizer.cpp:1862–2106

//

void Optimizer::checkSorts()
{
	SortNode* sort = rse->rse_sorted;
	const auto sortCount = sort ? sort->expressions.getCount() : 0;

	SortNode* project = rse->rse_projection;
	const auto projectCount = project ? project->expressions.getCount() : 0;

	// Check if a GROUP BY exists using the same fields as the project or sort:
	// if so, the projection can be eliminated; if no projection exists, then
	// the sort can be eliminated

	RecordSourceNode* subRse;
	AggregateSourceNode* aggregate;
	SortNode* group;

	if ((project || sort) &&
		rse->rse_relations.getCount() == 1 &&
		(subRse = rse->rse_relations[0]) &&
		(aggregate = nodeAs<AggregateSourceNode>(subRse)) &&
		(group = aggregate->group))
	{
		const auto map = aggregate->map;
		const auto groupCount = group->expressions.getCount();

		// If all the fields of the project are the same as all the fields
		// of the group by, get rid of the project

		if (project && projectCount == groupCount)
		{
			bool equal = true;
			for (unsigned i = 0; i < groupCount; i++)
			{
				const auto groupNode = group->expressions[i];
				const auto projectNode = project->expressions[i];

				if (!mapEqual(groupNode, projectNode, map))
				{
					equal = false;
					break;
				}
			}

			// We can now ignore the project, but in case the project is being done
			// in descending order because of an order by, do the group by the same way.
			if (equal)
			{
				setDirection(project, group);
				project = rse->rse_projection = nullptr;
			}
		}

		// If there is no projection, then we can make a similar optimization
		// for sort, except that sort may have fewer fields than group by

		if (!project && sort && sortCount <= groupCount)
		{
			bool equal = true;