Which SQL referential action is NOT supported by Oracle on foreign keys?

Introduction / Context:
Referential actions define how child rows respond when parent keys change or are deleted. Different DBMSs implement different subsets of these actions.

Given Data / Assumptions:

• We are considering Oracle Database behavior for foreign keys.
• Oracle supports ON DELETE CASCADE.
• Oracle sequences are created/dropped via CREATE SEQUENCE and DROP SEQUENCE (unrelated to FK actions).

Concept / Approach:
Historically and in mainstream usage, Oracle does not support ON UPDATE CASCADE on foreign keys. If a parent key must change, applications typically update child keys manually or redesign to avoid parent key updates (or use surrogate keys that never change).

Step-by-Step Solution:

Verification / Alternative check:
Oracle DDL will reject ON UPDATE CASCADE in a foreign key definition, requiring manual updates or triggers as a workaround.

Why Other Options Are Wrong:
ON DELETE CASCADE is supported.
CREATE SEQUENCE / DROP SEQUENCE are valid Oracle DDL statements, but are not referential actions.

Common Pitfalls:
Assuming all ANSI actions are supported on all platforms; Oracle differs from some other RDBMSs like PostgreSQL or MySQL in this respect.

Final Answer:
ON UPDATE CASCADE