MySQL Cookbook, 2nd Edition

Introduction

This chapter discusses the following kinds of database objects:

Stored routines (functions and procedures)

A stored function performs a calculation and returns a value that can be used in expressions just like a built-in function such as RAND(), NOW(), or LEFT(). A stored procedure performs calculations for which no return value is needed. Procedures are not used in expressions, they are invoked with the CALL statement. A procedure might be executed to update rows in a table or produce a result set that is sent to the client program. One reason for using a stored routine is that it encapsulates the code for performing a calculation. This enables you to perform the calculation easily by invoking the routine rather than by repeating all its code each time.

Triggers

A trigger is an object that is defined to activate when a table is modified. Triggers are available for INSERT, UPDATE, and DELETE statements. For example, you can check values before they are inserted into a table, or specify that any row deleted from a table should be logged to another table that serves as a journal of data changes. Triggers are useful for automating these actions so that you don’t need to remember to do them yourself each time you modify a table.

Events

An event is an object that executes SQL statements at a scheduled time or times. You can think of an event as something like a Unix cron job, but that runs within MySQL. For example, events can help you perform administrative tasks such as deleting ...