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Technicalstandard
Explain the difference between SQL and NoSQL databases, and when you'd pick each.
How to approach it
Frame it as a trade between strict structure and consistency on one side and flexibility and easy scaling on the other.
How a strong answer opens
“I'd frame it as a trade-off between strict structure and consistency on one side, and flexible structure and easy scaling on the other. The right pick depends on the data and how it's used.”
Outline of a strong answer
Try answering out loud for a few minutes before you open this.
- SQL: tables with fixed columns, joins, strong consistency
- NoSQL: documents, key-value or wide-column stores with flexible structure
- Pick SQL for payments, orders and anything needing exact accuracy
- Pick NoSQL for huge volumes of simple reads and writes, such as activity feeds
- Many products use both
- PM angle: reporting needs, data integrity, cost at scale
Where this question usually goes wrong
Calling NoSQL the modern choice and SQL outdated, or forgetting that many products use both for different jobs.
Learn the method
Data and databases in Module 6, Technical for PMs.
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