[ADD] Primary keys

Author: stivenramireza

classes/25-primary-keys.sql

@@ -0,0 +1,53 @@
+-- Generate a primary key using SERIAL or IDENTITY
+CREATE TABLE users (
+	user_id SERIAL PRIMARY KEY,
+	username VARCHAR(100)
+);
+
+CREATE TABLE users_2 (
+	user_id INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
+	username VARCHAR(100)
+);
+
+CREATE TABLE users_3 (
+	user_id INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
+	username VARCHAR(100)
+);
+
+CREATE TABLE users_4 (
+	user_id INTEGER GENERATED ALWAYS AS IDENTITY (START WITH 100 INCREMENT BY 2) PRIMARY KEY,
+	username VARCHAR(100)
+);
+
+-- Composite primary keys
+CREATE TABLE users_dual (
+	id_1 int,
+	id_2 int,
+	PRIMARY KEY (id_1, id_2)
+);
+
+SELECT *
+FROM users_dual;
+
+-- Generate UUID as primary key
+CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
+DROP EXTENSION "uuid-ossp";
+
+SELECT gen_random_uuid(), uuid_generate_v4();
+
+-- Generate a sequence
+DROP SEQUENCE user_sequence;
+CREATE SEQUENCE user_sequence;
+
+SELECT 
+	CURRVAL('user_sequence'), 
+	NEXTVAL('user_sequence'), 
+	CURRVAL('user_sequence');
+
+CREATE TABLE users_6 (
+	user_id INTEGER PRIMARY KEY DEFAULT NEXTVAL('user_sequence'),
+	username VARCHAR(100)
+);
+
+SELECT *
+FROM users_6;