Describe set operations UNION, INTERSECT, and EXCEPT
This tests advanced set logic in SQL. It is useful for merging and comparing datasets.
Why Interviewers Ask This
Set operations are powerful for combining and comparing results. Interviewers ask this to see if candidates know how to merge, find commonalities, or find differences between datasets efficiently.
How to Answer This Question
Define UNION as combining and removing duplicates. Define INTERSECT as finding common rows. Define EXCEPT as finding rows in first but not second. Mention compatibility requirements (same columns).
Key Points to Cover
- UNION merges and deduplicates
- INTERSECT finds common rows
- EXCEPT finds differences
- Requires compatible columns
Sample Answer
UNION, INTERSECT, and EXCEPT are set operations that combine results from two queries. UNION returns the distinct union, removing duplicates. INTERSECT returns only rows present in both result sets. EXCEPT returns rows f…
Common Mistakes to Avoid
- Ignoring column compatibility
- Confusing INTERSECT with JOIN
- Forgetting UNION removes duplicates
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