Which statement describes Update Cascade?

Which statement describes Update Cascade?

• A. The constraint that prevents updating a parent key if it is referenced.
• B. The constraint that sets child keys to NULL on update.
• C. When the parent key is updated, the change is propagated to all referencing rows.
• D. When the parent is deleted, all child rows are deleted.

Answer: (C)

Update Cascade means that when the value of a parent key changes, the database automatically updates all foreign keys in the child rows that reference that parent, so the references stay consistent. For example, if a department’s id changes from 5 to 50 and the child table has a foreign key pointing to that department with on update cascade, every row in the child table that referenced department 5 will have its dept_id updated to 50 as well. This preserves referential integrity without manual updates. The other concepts you might see are: restricting updates when a reference exists (preventing the change), updating child keys to NULL on a parent change (on update set NULL), or deleting a parent row cascading to delete its children (on delete cascade). Those describe different referential actions and not the automatic propagation of updates to foreign keys.

Update Cascade means that when the value of a parent key changes, the database automatically updates all foreign keys in the child rows that reference that parent, so the references stay consistent. For example, if a department’s id changes from 5 to 50 and the child table has a foreign key pointing to that department with on update cascade, every row in the child table that referenced department 5 will have its dept_id updated to 50 as well. This preserves referential integrity without manual updates.

The other concepts you might see are: restricting updates when a reference exists (preventing the change), updating child keys to NULL on a parent change (on update set NULL), or deleting a parent row cascading to delete its children (on delete cascade). Those describe different referential actions and not the automatic propagation of updates to foreign keys.