SQL Quiz — Joins, Indexes & Query Optimisation
SQL is the universal language of data. Knowing how to write efficient queries, design normalised schemas, and leverage indexes is a skill every backend and data engineer needs.
SQL proficiency is listed in nearly every backend and data engineering job description. Companies test query writing and optimisation in interviews — a verified score proves you're job-ready.
Sample Questions
3 of 10Q1.What is the difference between INNER JOIN and LEFT JOIN?
Q2.What does a database index improve, and what is its trade-off?
Q3.What is the difference between WHERE and HAVING in SQL?
Answer all 3 questions to see your score
Get your verified SQL score
Take the full 10-question quiz. Your score gets added to your developer resume as a verified skill badge — proof that you actually know SQL.
How verified skills work
Take the SQL quiz
10 adaptive questions covering real-world scenarios, not just syntax recall.
Your score is recorded
Skeelzy tracks your accuracy per skill over time — multiple attempts improve your verified score.
Add it to your resume
Your SQL accuracy appears as a verified badge on your public Skeelzy resume — proof for recruiters.