Function bson_max_combine

pg_documentdb/src/aggregation/bson_aggregates.c:999–1051

* Applies the "combine function" (COMBINEFUNC) for max. * takes two bsons * makes a new bson equal to the maximum */

 * makes a new bson equal to the maximum
 */
Datum
bson_max_combine(PG_FUNCTION_ARGS)
{
	MemoryContext aggregateContext;
	if (!AggCheckCallContext(fcinfo, &aggregateContext))
	{
		ereport(ERROR, errmsg(
					"Aggregate function invoked in non-aggregate context"));
	}

	/* Create the aggregate state in the aggregate context. */
	MemoryContext oldContext = MemoryContextSwitchTo(aggregateContext);

	pgbson *left = PG_GETARG_MAYBE_NULL_PGBSON(0);
	pgbson *right = PG_GETARG_MAYBE_NULL_PGBSON(1);
	pgbson *result;
	if (left == NULL)
	{
		if (right == NULL)
		{
			result = NULL;
		}
		else
		{
			result = PgbsonCloneFromPgbson(right);
		}
	}
	else if (right == NULL)
	{
		result = PgbsonCloneFromPgbson(left);
	}
	else
	{
		int32_t compResult = ComparePgbson(left, right);
		if (compResult > 0)
		{
			result = PgbsonCloneFromPgbson(left);
		}
		else
		{
			result = PgbsonCloneFromPgbson(right);
		}
	}

	MemoryContextSwitchTo(oldContext);

	if (result == NULL)
	{
		PG_RETURN_NULL();
	}

	PG_RETURN_POINTER(result);
}


/*