What are triggers? What types of triggers are there?

Triggers are special procedures in a database that automatically execute when certain events occur (for example, inserting, updating, or deleting data in a table).

Main types of triggers:

• By timing:

  • BEFORE (before the operation) — triggers that fire before the operation is executed.
  • AFTER (after the operation) — triggers that fire after the operation is completed.
  • INSTEAD OF — replaces the operation (usually used for views).

• By operation type:

  • INSERT — when new records are inserted.
  • UPDATE — when existing records are updated.
  • DELETE — when records are deleted.

For example, a BEFORE INSERT trigger can check the correctness of data before adding it, and an AFTER UPDATE trigger can keep a change log.

Triggers help automate business logic, ensure data integrity, and facilitate auditing without the need to change client code.