Reviewed by Aditya Kumar · Last reviewed 2026-03-24
**Situation**: A critical exec report was timing out at 30+ minutes; SLA was 5 minutes. **Task**: Diagnose and fix without changing business logic. **Action**: I ran EXPLAIN (ANALYZE) and found: (1) missing index on join key causing full table scan, (2) cross join that could be...
Red Flag: Saying 'I added an index' without explaining how you identified the bottleneck. Pro-Move: Mention EXPLAIN ANALYZE, predicate pushdown, and early filtering—shows systematic debugging.
This medium-level SQL question appears frequently in data engineering interviews at companies like Aarete, Accenture, Fossil Group, and 1 others. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join, sql) will help you answer variations of this question confidently.
Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.
Situation: A critical exec report was timing out at 30+ minutes; SLA was 5 minutes. Task: Diagnose and fix without changing business logic. Action: I ran EXPLAIN (ANALYZE) and found: (1) missing index on join key causing full table scan, (2) cross join that could be inner join with a filter, (3) filter in HAVING that could move to WHERE to reduce rows early, (4) unnecessary ORDER BY on a subquery. I added the index, rewrote the join, pushed predicates down, and removed redundant sort. Result: Runtime dropped to under 2 minutes; SLA met. I documented the changes and set up a query review process for similar reports.
Red Flag: Saying 'I added an index' without explaining how you identified the bottleneck. Pro-Move: Mention EXPLAIN ANALYZE, predicate pushdown, and early filtering—shows systematic debugging.
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According to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 4 companies. DataEngPrep.tech maintains an editor-reviewed database of 1,863 data engineering interview questions across 7 categories.