private boolean isRowNumberFunction(WindowNode node)
{
checkArgument(node.getWindowFunctions().size() == 1);
Symbol symbol = Iterables.getOnlyElement(node.getWindowFunctions().entrySet()).getKey();
Signature signature = node.getSignatures().get(symbol);
WindowFunction function = metadata.getExactFunction(signature).bindWindowFunction(ImmutableList.<Integer>of()).createWindowFunction();
return function instanceof RowNumberFunction;
}