Function ProcessOrderByStatements

pg_documentdb/src/opclass/index_support.c:3039–3181

static void
ProcessOrderByStatements(PlannerInfo *root,
						 IndexPath *path, int32_t minOrderByColumn,
						 int32_t maxOrderByColumn, bool isMultiKeyIndex,
						 const char *queryOrderPaths[INDEX_MAX_KEYS],
						 bool equalityPrefixes[INDEX_MAX_KEYS],
						 bool nonEqualityPrefixes[INDEX_MAX_KEYS],
						 int32_t pathSortOrders[INDEX_MAX_KEYS])
{
	int i = 0, sortDetailsIndex = 0;

	bool hasOrderBy = false;
	bool hasGroupby = false;
	bool isOrderById = false;
	List *sortDetails = GetSortDetails(root, path->path.parent->relid, &hasOrderBy,
									   &hasGroupby, &isOrderById);

	if (list_length(sortDetails) == 0)
	{
		return;
	}

	if (isMultiKeyIndex && hasGroupby)
	{
		/* We can't push down orderby on a multikey index if there is a group by */
		list_free_deep(sortDetails);
		return;
	}

	List *indexOrderBys = NIL;
	List *indexPathKeys = NIL;
	List *indexOrderbyCols = NIL;
	int32_t determinedSortOrder = 0;
	for (; i < minOrderByColumn; i++)
	{
		if (!equalityPrefixes[i])
		{
			/* No orderby on the column */
			list_free_deep(sortDetails);
			return;
		}
	}

	for (i = minOrderByColumn; i <= maxOrderByColumn; i++)
	{
		if (isMultiKeyIndex)
		{
			/* For a multi-key index, all order by related paths must have no filter specifications */
			if (nonEqualityPrefixes[i] || equalityPrefixes[i])
			{
				break;
			}
		}

		/* From this point, onwards, each path must either have an order or a valid filter
		 * for the path.
		 */
		if (pathSortOrders[i] != 0)