How many groups do two NULLs make?

Question

Accepted Answer

GROUP BY treats all NULL values as equal and places them in a single group. The two NULL rows form one group with a count of 2, just like the two 'East' rows form their own group. This is a deliberate exception to normal NULL comparison rules - normally NULL = NULL is UNKNOWN, but GROUP BY collapses NULLs together so aggregation can work on them.

id	region
1	East
2	NULL
3	NULL
4	East

East	2
NULL	2