Subqueries and NULL in a list

A query result can feed another query: one comparison value or an id list for membership. Examine why “not in the list” needs special care when NULL appears.

A subquery returns a value or set of values. IN tests membership; NOT IN needs care when its exclusion list can contain NULL.

Subqueries and NULL in a list: A subquery returns a value or set of values. IN tests membership; NOT IN needs care when its exclusion list can contain NULL.