Explain PostgreSQL roles and privileges system.

PostgreSQL uses roles for authentication and authorization.

Role Types:
• Login roles (users)
• Group roles (for organizing privileges)
• Superuser roles

Privileges:
• SELECT, INSERT, UPDATE, DELETE
• CREATE, DROP, ALTER
• USAGE, EXECUTE

Example:

CREATE ROLE developer;
GRANT SELECT, INSERT ON users TO developer;
CREATE ROLE john LOGIN PASSWORD 'password';
GRANT developer TO john;