How do I return my records grouped by NULL and NOT NULL?

Question

I have a table that has a processed_timestamp column -- if a record has been processed then that field contains the datetime it was processed, otherwise it is null.

Answer 1

I personally like Pax's solution, but if you absolutely require only one row returned (as I had recently), In MS SQL Server 2005/2008 you can "stack" the two queries using a CTE

with NullRows (countOf)
AS
(
    SELECT count(*) 
    FORM table 
    WHERE [processed_timestamp] IS NOT NULL
)
SELECT count(*) AS nulls, countOf
FROM table, NullRows
WHERE [processed_timestamp] IS NULL
GROUP BY countOf

Hope this helps