Counting null and non-null values in a single query

Question

I have a table

create table us
(
 a number
);

Now I have data like:

a
1
2
3
4
null
null
null
8
9

Now I need

Answer 1

SELECT SUM(NULLs) AS 'NULLS', SUM(NOTNULLs) AS 'NOTNULLs' FROM 
    (select count(*) AS 'NULLs', 0 as 'NOTNULLs' FROM us WHERE a is null
    UNION select 0 as 'NULLs', count(*) AS 'NOTNULLs' FROM us WHERE a is not null) AS x

It's fugly, but it will return a single record with 2 cols indicating the count of nulls vs non nulls.