Technical / ITData & AI▶ Live code
SQL & databases
Write confident queries, design simple schemas and answer the classic SQL interview questions.
Who it’s for: Developers, testers, analysts and support engineers — almost every IT role uses SQL.
Roadmap
What you’ll learn
Follow the modules in order. Finish a small project at the end of each one.
-
01
Querying
1 week- SELECT, WHERE, ORDER BY, LIMIT
- Aggregates and GROUP BY
- HAVING
- NULL handling
-
02
Joins
1 week- INNER, LEFT, RIGHT joins
- Self joins
- Subqueries
- UNION
-
03
Advanced
2 weeks- Window functions (RANK, DENSE_RANK)
- CTEs
- Indexes and EXPLAIN
- Transactions and ACID
-
04
Design
1 week- Keys and relationships
- Normalisation
- ER diagrams
- Choosing data types
Tools
Tools & skills to learn
- MySQL
- PostgreSQL
- SQLite
- DBeaver
Certifications
Useful certifications
- HackerRank SQL skill certificateFree online test
Certificates support your profile — interviewers still ask what you built. Check current fees and rules on the official site.
Practice
Projects to build
Put these on your resume — they give you real stories for interviews.
- 1Library database with sample queries
- 2Top-N per group report
- 3Duplicate detection and clean-up script
Live code
Practise right here
Run examples and try the 🏆 challenges — your answers are checked automatically.
Preview
Console
Sample tables: employees(id, name, dept_id, salary, joined) · departments(id, name) · users(id, email)
Result
Press Run to see the result.
Output
Code runs only in your browser. Press Ctrl/⌘ + Enter to run. Pick a 🏆 Challenge from the Example list to get your answer checked automatically.
Next steps
Interview & jobs
Get job alerts for this field