Databases
SQL queries, joins, normalisation, indexing, transactions and NoSQL modelling.
What you are tested on
- SELECT, JOIN and GROUP BY
- Normalisation
- Indexes and query plans
- Transactions and ACID
- MongoDB and NoSQL modelling
Practice problems (13 in total)
- Normalize a Denormalized Orders TableMedium
- Detect a Deadlock CycleHard
- Index Selectivity EstimatorEasy
- Highest Paid per DepartmentMedium
- Running TotalEasy
- Find Duplicate EmailsEasy
- Second Highest SalaryEasy
- Customers with Multiple OrdersMedium
- Employee–Department JoinMedium
- GROUP BY … HAVINGEasy
- LEFT JOIN with NULLsMedium
- RANK and DENSE_RANKMedium
Roadmaps
How your Databases rating works
You start at 1200. Each timed, rated test moves your Databases rating up or down, the way chess ratings move. Recruiters see the number and the band (Beginner, Intermediate, Advanced or Expert), so they can judge your skill before reading a résumé. See a sample profile.
Questions about Databases
Is SQL asked in fresher interviews?
Almost always for backend, data and QA roles, from simple joins to indexing questions.
SQL or NoSQL first?
SQL first: it teaches the thinking, and NoSQL then makes more sense.