Stored Procedures vs. Functions

The Difference

**Function**: Returns a value. Can be used in SELECT statements.

**Stored Procedure**: Executes logic. Can have side effects (INSERT, UPDATE).

CREATE FUNCTION get_customer_total(cust_id INT) RETURNS NUMERIC AS $$

SELECT SUM(amount) FROM orders WHERE customer_id = cust_id;

$$ LANGUAGE SQL;

-- Usage

SELECT name, get_customer_total(id) FROM customers;

Keep your functions pure (no side effects) for easier testing and debugging.

*Day 85: Triggers—The Automatic Reaction.*