Learn to create and use stored procedures and functions to encapsulate logic.
Stored Procedures and Functions are blocks of pre-compiled SQL code that are stored in the database and can be executed on demand. They are used to encapsulate and reuse business logic, improve performance, and enhance security. A Stored Procedure is a set of SQL statements that can be executed as a single unit. It can accept input parameters and return output parameters. For example, you could create a procedure to hire a new employee that takes 'name' and 'dept_id' as input, performs multiple `INSERT` statements into different tables, and returns the new 'employee_id' as output. Procedures are called using the `CALL` or `EXECUTE` command. A User-Defined Function (UDF) is similar to a procedure but with a key difference: it must always return a single value and is typically used within SQL statements, just like built-in functions (e.g., `AVG()`, `CONCAT()`). For example, you could create a function that takes a 'product_id' as input and returns the current inventory level. You could then use this function directly in a `SELECT` statement: `SELECT product_name, get_inventory_level(product_id) FROM products;`. Both procedures and functions offer benefits like reduced network traffic (since only the call is sent, not the entire SQL block), centralized logic (making maintenance easier), and improved security (you can grant users permission to execute a procedure without giving them access to the underlying tables).