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

In Oracle

SELECT COUNT(*), COUNT(TIME_STAMP_COLUMN)
FROM TABLE;

count(*) returns the count of all rows

count(column_name) returns the number of rows which are not NULL, so

SELECT COUNT(*) - COUNT(TIME_STAMP_COLUMN) NUL_COUNT,
                  COUNT(TIME_STAMP_COLUMN) NON_NUL_COUNT
FROM TABLE

ought to do the job.

If the column is indexed, you might end up with some sort of range scan and avoid actually reading the table.