SQL vs NoSQL
maang.io System Design Series
"SQL vs NoSQL" is the most common — and most misunderstood — database question in interviews. This deep dive replaces the false binary with a framework: relational vs the four NoSQL families (key-value, document, wide-column, graph), ACID vs BASE, rigid vs flexible schema, and vertical vs horizontal scaling. The answer is almost always "it depends — here's on what."
This deep dive comes in three parts:
- Foundations & Core Concepts — the families, ACID vs BASE, and the scaling models.
- Internals — schema-on-read, join-vs-embed, and polyglot persistence, with worked examples.
- Interview — Staff/Principal Q&A: picking a store and defending the trade-offs.