Beginner~1h
Set Operations in SQL & DatabasesInterview Readiness Check
UNION vs UNION ALL performance, INTERSECT for overlap, EXCEPT for difference, ORDER BY rules.
unionunion allintersectexceptminusset operations
Learning path
Try a sample question
UNION vs UNION ALL — when should you use UNION ALL?
A.When you want to eliminate duplicate rows across the two result sets
B.UNION ALL is only valid when both queries return the same number of rows
C.When you know there are no duplicates, or duplicates are intentional — UNION ALL skips the deduplication sort/hash step and is significantly faster
D.When combining results from tables with different column counts
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What this module tests
- Conceptual understanding of set operations fundamentals
- Trade-offs and design decisions in real system scenarios
- union and union all — applied knowledge
- Interview-style reasoning and explanation quality
Free to start
Take the Set Operations check →
10 questions · Dimension scoring · AI coach feedback · Shareable result
Test your knowledge — free →No credit card · Takes 10–15 min
Frequently asked questions
- What does the Set Operations check test?
- The check covers union vs union all performance, intersect for overlap, except for difference, order by rules. Questions span beginner to advanced difficulty and test both conceptual understanding and practical trade-off reasoning.
- What keywords should I know for Set Operations?
- Key concepts include: union, union all, intersect, except, minus, set operations. These frequently appear in sql & databases interviews at product and infrastructure companies.
- How many questions are in the check?
- Each check has 10 questions — a mix of MCQ and short-answer. You get scored by dimension (e.g., scalability, consistency) so you know exactly where to focus.
- How long does it take to study Set Operations?
- Most engineers spend around 1 hours on this module. The check itself takes about 10–15 minutes. You can retake it up to 3 times per day.
- What prerequisite knowledge do I need before Set Operations?
- Set Operations builds on Joins & Relationships. Complete those first for the best results.
- Is union, union all, intersect covered?
- Yes. The Set Operations module covers union, union all, intersect among other key concepts. The check includes questions that reflect real sql & databases interview patterns.