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Lesson 13 of 14

8. SQL vs NoSQL

1
The picture to keep in your head
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8.1 What are tables, rows and keys?
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8.2 What does ACID mean?
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8.3 What is normalisation, and what are joins?
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8.4 What kinds of NoSQL databases are there?
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8.5 What's the difference between schema-on-write and schema-on-read?
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8.6 Why does NoSQL often duplicate data and avoid joins?
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8.7 How do you choose between SQL and NoSQL?
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Memory card and where the analogy breaks
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Practice: five levels
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Interview questions
12
Solutions
13
Sources
14
Code lab
8. SQL vs NoSQL

Sources

3 min read+10 XP

Source notes

  • ACID: the term was introduced by Theo Härder and Andreas Reuter, "Principles of Transaction-Oriented Database Recovery", ACM Computing Surveys, 1983.
  • Normal forms: E. F. Codd's relational model papers (1970 onward).
  • Wide-column design: Fay Chang et al., "Bigtable: A Distributed Storage System for Structured Data", OSDI 2006; Apache Cassandra documentation (partition keys and clustering columns).
  • Key-value at scale: Giuseppe DeCandia et al., "Dynamo: Amazon's Highly Available Key-value Store", SOSP 2007.
  • PostgreSQL JSON support (json and jsonb types): PostgreSQL documentation.
  • Transactions in NoSQL databases: for example, MongoDB multi-document transactions and DynamoDB transactions, per their official documentation.
  • SQLite enforces foreign keys only when PRAGMA foreign_keys = ON is set: SQLite documentation.
  • Level 2 numbers are illustrative assumptions; arithmetic computed 2026-10-08.
  • Level 3 and Level 4 code: tested 2026-10-08 (code/ch08_sql_nosql.py, all checks pass).