Should I use PostgreSQL for a startup backend with lots of joins?

Yes — PostgreSQL is usually a very good choice for a startup backend with lots of joins.

Why PostgreSQL fits well

• Strong relational model: Joins are a first-class use case.
• Great query planner: It generally handles complex multi-table queries very well.
• ACID transactions: Safer for business-critical data.
• Rich indexing options: B-tree, GIN, GiST, partial indexes, expression indexes, etc.
• Flexible enough: You can still use JSONB for parts of the app that don’t fit cleanly into tables.

When it’s especially a good idea

Use PostgreSQL if:

• your data is naturally relational,
• you need consistent data and transactions,
• you expect to write a lot of reporting/analytics-style SQL,
• your app will need complex filtering, sorting, and joins.

What to watch out for

• Bad schema design can still make joins slow.
• You’ll want to pay attention to:
  • indexing foreign keys,
  • query plans (EXPLAIN ANALYZE),
  • avoiding unnecessary N+1 queries in the application,
  • denormalizing only when there’s a measured need.

Startup perspective

PostgreSQL is often the safest default for startups because it:

• scales far enough for many products,
• has excellent tooling and community support,
• avoids premature optimization into NoSQL systems that complicate joins.

Bottom line

If your backend has lots of joins, PostgreSQL is one of the best choices. Start there unless you have a very specific reason not to.

If you want, I can also help you compare PostgreSQL vs MySQL vs MongoDB for your specific backend use case.