What is the difference between SQL and NoSQL databases?
SQL databases are relational, store data in tables with a fixed schema, and are strong on consistency and complex queries. NoSQL databases are non relational, store data in flexible formats like documents or key value pairs, and scale out easily for huge volumes. Choose SQL for structured data and complex relationships, and NoSQL for flexible schemas and massive scale.
- SQL databases are relational with fixed schemas and strong consistency.
- NoSQL databases are flexible, often schema less, and scale horizontally.
- Choose SQL for structured related data and NoSQL for large or evolving unstructured data.
SQL databases
These use tables with rows and columns and a defined schema. They shine when data is structured, relationships matter, and you need strong consistency, such as banking. Examples include MySQL and PostgreSQL.
NoSQL databases
These trade the rigid schema for flexibility and easy horizontal scaling. They fit rapidly changing data and very high volume, such as social feeds or logs. Examples include MongoDB and Cassandra.
Quick comparison
- Schema: SQL is fixed, NoSQL is flexible.
- Scaling: SQL scales up, NoSQL scales out easily.
- Best for: SQL for relationships and consistency, NoSQL for scale and flexibility.
Avoid saying one is simply better. The strong answer is it depends on the use case, then give one example each. Mentioning that many real systems use both together shows mature thinking.
Frequently asked questions
When should you choose NoSQL?
Choose NoSQL for very large scale, flexible or changing schemas, and high write throughput, such as caching, logs, or document heavy applications.
Do NoSQL databases support transactions?
Many modern NoSQL databases support transactions, but historically they favoured availability and eventual consistency over strict ACID guarantees.
Common follow up questions
Related interview questions
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