CASE WHEN NULL - will this branch fire?

Question

Accepted Answer

Simple CASE compares using equality (region = NULL internally), and NULL = NULL evaluates to UNKNOWN, not TRUE. Because the WHEN NULL branch is never satisfied, execution falls through to ELSE 'Other'. To catch NULLs in a CASE you must use the searched form: CASE WHEN region IS NULL THEN 'Unknown' ... END. This is one of the most common traps when converting simple CASE to handle NULLs.