How to Practice SQL Interview Questions
A practical guide to practicing SQL interview questions. Covers joins, window functions, aggregation, and optimization. Shows how to explain your approach and score your answers. Links to SQL tracks.
Core SQL topics that appear in interviews
Joins, GROUP BY / HAVING, window functions, subqueries or CTEs, NULL handling, and basic performance come up constantly. Analyst roles emphasize readable queries and correct grain; engineering roles may push indexing harder.
Practice explaining the approach before the full query. Interviewers listen for how you think about duplicates, ties, and missing keys.
How to explain joins and window functions
For joins, state the grain of each table, the join keys, and whether you need inner or outer. Call out fan-out risk when one-to-many joins inflate counts.
For windows, name the partition, order, and frame. Say what RANK vs ROW_NUMBER vs DENSE_RANK does for ties before writing syntax.
Optimization and indexing questions
Talk about reading the plan at a high level: filters early, sensible indexes, avoiding unnecessary sorts. Mention when a covering index or rewriting a correlated subquery helps.
Stay practical — premature micro-optimization without a slow query story scores lower than clear correctness.
How to score SQL answers
Score correctness of the pattern, clarity of explanation, and edge-case awareness (NULLs, ties, empty groups). Deduct for jumping to code without stating grain or assumptions.
Retry weak prompts by writing a one-sentence approach first, then the query sketch.
Recommended practice tracks
Browse the SQL group for joins, windows, aggregations, and performance tracks. Use SQL for Analysts when your loop is analytics-focused rather than DBA-heavy.
First two questions on any track include full feedback so you can tighten explanations quickly.
Practice approach
Four prompts twice a week: two joins/aggregations, one window, one edge-case or optimization. Speak the approach for 20 seconds before typing.
Keep a short cheat sheet of patterns (anti-join, running total, top-N per group) and force yourself to name the pattern out loud.