presto-main/src/main/java/io/prestosql/sql/planner/optimizations/WindowFilterPushDown.java/WindowFilterPushDown/canOptimizeWindowFunction
class WindowFilterPushDown:        private boolean canOptimizeWindowFunction(WindowNode node)
        {
            if (node.getWindowFunctions().size() != 1) {
                return false;
            }
            Symbol rowNumberSymbol = getOnlyElement(node.getWindowFunctions().entrySet()).getKey();
            return node.getWindowFunctions().get(rowNumberSymbol).getResolvedFunction().getFunctionId().equals(rowNumberFunctionId);
        }