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

Another MySQL method is to use the CASE operator, which can be generalised to more alternatives than IF():

SELECT CASE WHEN processed_timestamp IS NULL THEN 'NULL' 
            ELSE 'NOT NULL' END AS a,
       COUNT(*) AS n 
       FROM logs 
       GROUP BY a