SQL Interview Questions — Queries, Joins & Optimization
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SQL Interview Questions — Queries, Joins & Optimization
SQL appears in almost every campus pipeline: standalone DB rounds, backend pairing interviews, and data analyst screenings. Indian service companies often include 10–15 SQL questions in technical assessments.
Must-know concepts
Joins: INNER, LEFT, RIGHT, FULL — know when rows drop or duplicate.
Aggregations: GROUP BY with HAVING filters after grouping.
Window functions: ROW_NUMBER, RANK, LAG/LEAD for ranking and time-series.
Indexing: B-tree basics, when indexes help vs hurt writes.
Normalization: 1NF–3NF and when denormalization is justified.
Practice approach
Use SQLBolt, LeetCode SQL study plan, and HackerRank SQL tracks. Write queries without GUI autocomplete to simulate interview pressure.
Sample scenario questions
- Second highest salary per department
- Monthly active users with cohort retention
- Detect duplicate email registrations
- Explain EXPLAIN plan for a slow query
Review SQL interview questions sorted by difficulty.
Related resources
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