| Feature | MongoDB | PostgreSQL |
|---|---|---|
| Database Type | NoSQL document store | Relational SQL database |
| Schema | Flexible, schema-less | Strict schema |
| Query Language | JSON-like queries | SQL |
| Transactions | Multi-document ACID (newer) | Full ACID compliance |
| Joins | Limited ($lookup) | Powerful, native |
| Scalability | Horizontal scaling (sharding) | Vertical scaling; horizontal with tools |
| Use Cases | Flexible data, rapid development | Complex queries, relational data |