How do I choose between PostgreSQL, MySQL and MongoDB for my project?

Short answer

  1. Choose PostgreSQL if you have complex relational data, ACID transactions and want maximum extensibility (JSON, full-text search, advanced functions).
  2. Choose MySQL if your app is already built on MySQL, if you want a large ecosystem and wide compatibility with web frameworks.
  3. Choose MongoDB if your data is JSON documents with variable schema (products with different attributes, CMS content, telemetry).
  4. Practical rule: tabular data with relations → PostgreSQL; LAMP/LEMP web apps → MySQL; flexible/unstructured data → MongoDB.

What the standard / legislation says

  • ACID: PostgreSQL and MySQL support full ACID transactions; MongoDB supports them from v4.0 (single-doc native, multi-doc with sessions).
  • Licenses: PostgreSQL = BSD license (fully free); MySQL = dual-license GPL + Oracle Commercial; MongoDB = SSPL (cloud restrictions).
  • OLTP Performance: MySQL is slightly faster for simple write-heavy workloads; PostgreSQL wins on complex queries.
  • Native JSON: PostgreSQL has JSONB (indexable, fast); MongoDB has native BSON; MySQL has JSON but more limited.

Practical examples

  • PostgreSQL example: multi-tenant SaaS app with invoices, clients and transactions — clear relations, complex JOINs, RLS per tenant.
  • MySQL example: blog/CMS platform with WordPress, Drupal or Laravel — large ecosystem, easy migration, cheap hosting.
  • MongoDB example: marketplace product catalog with 200+ different attributes per product — flexible schema, automatic sharding.

Common mistakes

  • Mistake 1: using MongoDB for everything — MongoDB isn't suitable for financial transactions or complex SQL reporting.
  • Mistake 2: migrating from MySQL to PostgreSQL without testing — SQL syntaxes differ; string and date functions behave differently.
  • Mistake 3: choosing a database by popularity, not use-case — PostgreSQL is more popular, but MySQL may be simpler for your needs.

How 4database.net helps you

  • 4database.net supports managed PostgreSQL, MySQL and MongoDB — you can test both and migrate easily with one-click export/import.
  • Comparative monitoring: see slow queries on both databases and compare real performance on your data.
  • AI Copilot generates queries specific to the chosen engine — PostgreSQL JSONB, MySQL JSON or MongoDB aggregation pipeline.
  • Assisted migration between databases with step-by-step guide and automatic schema validation.
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See also