SQL and Query Optimization
Why this subject matters: SQL is asked in almost every data role interview — Data Analyst, Data Scientist, Data Engineer — often as a live query-writing round, not just theory. Query optimization specifically separates candidates who can write correct SQL from those who can write SQL that scales.
Learn SQL Quickly: A Beginner's Guide to Learning SQL, Even If You're New to Databases
A fast, no-fluff introduction to SQL for absolute beginners — strips away database theory and focuses on writing working queries from the first chapter.
SQL All-In-One for Dummies
A broad, well-organized reference spanning SQL fundamentals, database design, and administration — useful as a single go-to book covering multiple database systems.
SQL and NoSQL Interview Questions
A focused bank of interview-style SQL and NoSQL questions — good for a final revision pass before a data role interview rather than first-time learning.
MongoDB Applied Design Patterns
Practical, real-world use cases for modeling data in MongoDB — a useful step beyond SQL for understanding how a leading NoSQL database is actually designed and queried.
