SQL Interview Rounds: What to Expect and How to Prepare

SQL rounds appear in data analyst, data engineer, backend and product analyst interviews. They are usually more predictable than candidates expect.

Common question types

• Joins across two or three tables, including LEFT JOIN edge cases with NULLs
• GROUP BY with HAVING
• Window functions: ROW_NUMBER, RANK, running totals, LAG/LEAD
• Finding duplicates or the Nth highest value
• Date handling: month-over-month, retention and cohort queries

How to prepare

1. Practise writing queries in a plain editor, without autocomplete.
2. Say your approach out loud before you write: which tables, which join, which grain.
3. Always check edge cases: empty tables, NULLs, ties.
4. Review your practice sessions. A recap of what you were asked and how you answered (for example from ClapAssist, which has a technical/SQL mode) shows you which patterns you keep getting wrong.

On the day

Clarify the schema first, state your assumptions and write readable SQL with clear aliases. Interviewers value clarity over clever one-liners.