[ADD] Functions intro

Author: stivenramireza

classes/32-functions.sql

@@ -0,0 +1,21 @@
+-- Functions intro
+SELECT GREATEST(1, 2, 30, 5);
+
+SELECT COALESCE(NULL, 'Hello world!');
+
+CREATE OR REPLACE FUNCTION greet_employee(employee_name VARCHAR)
+RETURNS VARCHAR
+AS $$
+-- DECLARE
+BEGIN
+	RETURN 'Hello ' || employee_name;
+END;
+$$
+LANGUAGE plpgsql;
+
+SELECT greet_employee('Stiven');
+
+SELECT
+	first_name,
+	greet_employee(first_name)
+FROM employees;