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Predict the output of SQL joins (INNER, LEFT, RIGHT) on dataset containing 0, NULL, and 1

SQLmedium0.5 min readPremium
Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Wolters Kluwer
Key Concepts Tested
joinsql
Expert AnswerPremium
90 wordsInterview-ready
NULL in joins: NULL = NULL is UNKNOWN, so INNER JOIN excludes null keys. LEFT JOIN: left rows with null key get null for right side. With 0, NULL, 1: INNER on 0 and 1 only; NULL never matches. LEFT: all left rows; right null for no match. Be explicit with COALESCE in join keys if nulls should match. **Why it matters**: Design choices compound at scale—wrong approach can cause 100× overhead. **Scalability trade-offs**: Profile before optimizing; validate on sample then full....
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