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

SQL Server (starting with 2012):

SELECT IIF(ISDATE(processed_timestamp) = 0, 'NULL', 'NON NULL'), COUNT(*)
FROM MyTable
GROUP BY ISDATE(processed_timestamp);

Answer 2

In T-SQL (MS SQL Server), this works:

SELECT
  CASE WHEN Field IS NULL THEN 'NULL' ELSE 'NOT NULL' END FieldContent,
  COUNT(*) FieldCount
FROM
  TheTable
GROUP BY
  CASE WHEN Field IS NULL THEN 'NULL' ELSE 'NOT NULL' END