25. Using Triggers
In this chapter, you learn what triggers are, why they are used, and how. You also look at the syntax for creating and using them.
MariaDB statements are executed when needed, as are stored procedures. But what if you want a statement (or statements) to be executed automatically when events occur? For example:
• Every time a customer is added to a database table, check that the phone number is formatted correctly and that the state abbreviation is in uppercase.
• Every time a product is ordered, subtract the ordered quantity from the number in stock.
• Whenever a row is deleted, save a copy in an archive table.
All these examples need to be processed automatically whenever a table change occurs. And that ...