PostgreSQL vs MySQL vs MongoDB
A practical three-way comparison of the most widely deployed databases — when to pick a relational engine vs a document store, and how the two big SQL options stack up.
Feature Comparison
| Feature | PostgreSQL | MySQL | MongoDB |
|---|---|---|---|
| Type | Relational | Relational | Document |
| Transactions | Full ACID | ACID (InnoDB) | Multi-doc ACID |
| Schema | Strict + flexible with JSONB | Strict | Flexible |
| Query language | SQL (rich) | SQL | MongoDB Query Language |
| JSON support | Excellent (JSONB + indexes) | Good JSON type | Native |
| Scaling | Vertical + read replicas | Vertical + Vitess | Native horizontal sharding |
| Performance | Great for complex queries | Great for simple lookups | Great for document retrieval |
| Community | Massive | Massive | Large |
| Cloud offerings | AWS RDS, Supabase, Neon | AWS RDS, PlanetScale | Atlas, DocumentDB |
| Best for | Complex data + analytics | Simple web apps | Flexible unstructured data |
Capability Chart
Verdict
Choose PostgreSQL when:
- You need rich SQL, CTEs, window functions, and analytics
- Data integrity and strong ACID guarantees matter
- You want both relational rigor and JSONB flexibility
- Extensions (PostGIS, pgvector, TimescaleDB) fit the use case
Choose MySQL when:
- Classic LAMP / web app workloads with simple queries
- Read-heavy traffic with many replicas
- Managed options like PlanetScale or Aurora MySQL fit your team
- Huge amount of existing tooling and developer familiarity
Choose MongoDB when:
- Schema evolves rapidly or is deeply nested
- You need native horizontal sharding out of the box
- Document-shaped data beats joins for your access patterns
- Atlas fits as a managed, multi-cloud solution
Frequently Asked Questions
Which is better — PostgreSQL, MySQL, or MongoDB?
Default to PostgreSQL: best-in-class for relational data, full ACID, strong JSON support, and extensions (pgvector for AI). Pick MySQL if you have existing MySQL expertise or specific tooling. Pick MongoDB only when your data is genuinely document-shaped (variable schemas, deeply nested) and you do not need cross-document transactions.
Should I use MongoDB or PostgreSQL JSONB for flexible data?
PostgreSQL JSONB usually wins for most use cases — you get full JSON flexibility AND relational consistency AND SQL joins in one engine. Reach for MongoDB only when 100% of your data is document-shaped, you need horizontal sharding from day one, or your team is much stronger in MongoDB than SQL.
Does MySQL still make sense in 2026?
Yes for existing MySQL shops and WordPress/PHP ecosystems, where MySQL tooling is best supported. For greenfield projects, PostgreSQL is usually the stronger pick — better JSON, better extensibility, better SQL standard compliance. The performance gap has closed; the feature gap remains.
How do scaling characteristics compare?
PostgreSQL and MySQL scale vertically very well; horizontal scaling requires read replicas or sharding tooling (Citus, Vitess). MongoDB ships with native sharding built into the engine. For 99% of apps, vertical scaling on a managed PostgreSQL (RDS, Cloud SQL, Supabase) handles 10K+ QPS without sharding.