When to use SQL vs NoSQL

SQL databases (PostgreSQL) use strict tables and relationships, which is great when data is connected and must stay consistent, like orders, payments, and users. NoSQL databases (MongoDB) use flexible documents, which is great when the data shape changes often or is naturally nested, like logs, content, or prototypes.

Choose SQL (PostgreSQL) when:
- Data has clear relationships (users -> orders -> items)
- You need JOINs and strong consistency
- Example: e-commerce, banking, most web apps

Choose NoSQL (MongoDB) when:
- The data shape changes often
- Data is nested / self-contained
- Example: content feeds, logs, chat messages

Not sure? PostgreSQL is a safe default.