In PostgreSQL, a role is a central concept for managing users and permissions.

🔹 What is a Role?

A role is an entity that can:

• Own database objects (tables, views, etc.)
• Have permissions (SELECT, INSERT, etc.)
• Login into the database (if allowed)

👉 In simple words: Role = User + Permissions system

🔹 Types of Roles

There are mainly two types:

1. Login Role (User)

• Can log in to the database
• Example: student1, admin

2. Group Role

• Cannot log in
• Used to assign permissions to multiple users

🔹 Why We Use Roles?

Roles are used for security and management:

✅ 1. Access Control

• Restrict who can access data

✅ 2. Permission Management

• Assign permissions once to a role, then assign role to many users

✅ 3. Better Organization

• Separate admin, teacher, student roles

✅ 4. Data Security

• Prevent unauthorized changes

🔹 Syntax: Create Role

Basic Syntax:

CREATE ROLE role_name;

🔹 Create Role with Login (User)

CREATE ROLE student1
WITH LOGIN
PASSWORD '1234';

🔹 Create Role with Common Options

CREATE ROLE teacher
WITH 
LOGIN
PASSWORD 'securepass'
CREATEDB
CREATEROLE;

🔹 Important Options

🔹 Example

CREATE ROLE admin_user
WITH LOGIN
PASSWORD 'admin123'
SUPERUSER;

🔹 Grant Role to Another User

GRANT teacher TO student1;

🧪 Lab: Understanding Roles using dvdrental Database

🎯 Learning Outcomes

Students will:

• Understand what a role is
• Create roles with different privileges
• View and analyze roles
• Change database ownership
• Understand ownership vs permissions

🔹 Step 1: Create a New Role (User)

Before assigning ownership, the role must exist.

CREATE ROLE senior_admin 
WITH LOGIN 
PASSWORD 'secure_pass123';

🧠 Concept:

• LOGIN → makes it a user
• Without LOGIN → it is just a group role

👉 Key Idea: In PostgreSQL, there is no separate "user" concept — everything is a role

🔹 Step 2: View All Roles

SELECT rolname FROM pg_roles;

✔️ This retrieves all roles in the server.

🔍 Understanding pg_roles

• It is a system catalog view

• Stores:

  • Users
  • Groups
  • Privileges
  • Role attributes

📊 Better Query (Detailed View)

SELECT 
    rolname, 
    rolsuper, 
    rolcreaterole, 
    rolcreatedb, 
    rolcanlogin
FROM pg_roles;

🧠 Column Understanding:

🎯 Filter Only Users

SELECT rolname
FROM pg_roles
WHERE rolcanlogin = true;

🖥️ Alternative (psql)

\du

🔹 Step 3: Assign Ownership of dvdrental

ALTER DATABASE dvdrental OWNER TO senior_admin;

🧠 Concept: Ownership

Ownership is very powerful:

• Owner can:

  • Drop database
  • Rename database
  • Grant permissions

👉 Ownership ≠ Normal permissions

❗ Database Ownership vs Table Ownership

After running:

ALTER DATABASE dvdrental OWNER TO senior_admin;

✔️ Only the database owner changes

❌ Tables like:

• film
• actor
• customer

👉 DO NOT change owner automatically

🔹 Step 4: Verify Ownership

In terminal:

\l

Expected Output:

⚠️ Permissions Requirement

Only:

• Superuser
• OR current database owner

👉 can run ALTER DATABASE

Otherwise: ❌ permission denied