Trigger

A trigger is database code that executes automatically when specific events (INSERT/UPDATE/DELETE) occur, used for auditing, cascading, and constraints.

Purpose

To execute logic automatically on data changes without explicit application calls.

Mechanism

BEFORE/AFTER × row-level/statement-level triggers. When the event fires, the trigger function runs automatically. Commonly used for audit logs, cascading updates, and complex constraint checks. But implicit execution is hard to debug and may cascade unexpectedly.

Use cases

Data-change audit logs
Cascading updates and sync
Complex constraint checks
Automatic materialized-view refresh

Examples

Input

AFTER UPDATE ON users → log change

Output

Change recorded automatically

Audit trigger

Common errors

Trigger cascades cause recursion and deadlocks: Limit trigger depth and avoid cycles

Related terms

Stored Procedure

A stored procedure is a precompiled SQL program stored in the database that can be invoked on demand, reducing network round trips and SQL-injection risk.

A view is a stored query definition (a virtual table) holding no data, computed dynamically at query time, used to simplify queries, isolate security, and abstract.

A transaction is a group of operations executed as a single logical unit satisfying ACID properties — all or nothing.

References