Oracle: How to count null and non-null rows

Question

I have a table with two columns that might be null (as well as some other columns). I would like to count how many rows that have column a, b, both and neither colu

Answer 1

It can be accomplished in Oracle just in 1 row:

SELECT COUNT(NVL(potential_null_column, 0)) FROM table;

Function NVL checks if first argument is null and treats it as value from second argument.