How do SQL triggers differ from stored procedures?

SQL triggers and stored procedures serve different purposes in database management, though both are used to automate actions. A trigger is a special type of stored procedure that automatically executes in response to specific database events, such as INSERT, UPDATE, or DELETE operations on a table. Triggers are tied directly to table events and cannot be manually invoked. In contrast, a stored procedure is a precompiled set of SQL statements that performs a specific task when explicitly called by a user, application, or another procedure. Stored procedures are reusable blocks of code that accept parameters, return results, and can include complex logic.

The key difference lies in execution control. Triggers are event-driven and run implicitly when their defining event occurs. For example, a trigger might log changes to an audit table every time a row is updated. This automatic behavior ensures consistency but can make debugging harder, as triggers fire without direct developer intervention. Stored procedures, on the other hand, require explicit invocation. For instance, a procedure might calculate monthly sales totals when called by a reporting tool. Developers control when and how procedures run, which provides flexibility but requires manual integration into workflows.

Another distinction is their scope and use cases. Triggers are typically used for enforcing business rules, maintaining audit trails, or synchronizing data across tables. For example, a trigger might prevent deleting a customer record if associated orders exist. However, overusing triggers can lead to performance issues, especially if they cascade or execute complex logic. Stored procedures are better suited for tasks like data transformation, batch processing, or encapsulating frequently used queries. For example, a procedure might validate user input, update multiple tables, and return a success/failure status. Procedures also support transactions and error handling more explicitly, while triggers operate within the transaction of the event that fired them, making rollbacks or error propagation less straightforward.