1. What is PostgreSQL?
PostgreSQL is an open-source relational database management system (RDBMS) known for its extensibility and standards compliance. It supports both SQL and non-SQL (NoSQL) queries.
2. Explain the difference between PRIMARY KEY and UNIQUE constraint in PostgreSQL.
The PRIMARY KEY constraint uniquely identifies each record in a table and cannot contain NULL values. The UNIQUE constraint ensures that all values in a column are distinct, but it can contain NULL values.