Answer
Triggers are special stored procedures that automatically execute in response to DML events (INSERT, UPDATE, DELETE) or certain DDL operations.
AFTER triggers:
- Fire after the base operation logically succeeds but before the transaction commits.
- Often used for auditing, logging, or enforcing complex constraints that span multiple tables.
- Run within the transaction, so failures can cause rollbacks and increase latency.
INSTEAD OF triggers:
- Fire instead of the original DML operation.
- Commonly used on views to simulate complex update logic or route changes to multiple underlying tables.
- Give full control over how changes are applied.
Both types must be designed carefully to avoid recursion, hidden performance issues, and unexpected side effects.