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Solve medium-level SQL questions involving two tables with null values - LEFT JOIN, RIGHT JOIN, INNER JOIN

SQLmedium0.4 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
Myntra
Key Concepts Tested
joinsql
Expert AnswerPremium
81 wordsInterview-ready
With nulls in join keys: INNER excludes null keys (no match). LEFT: keeps left rows, null for right when no match or when key is null. RIGHT: mirror of LEFT. Test: create small tables with 0, NULL, 1; run each join; observe. Use COALESCE in ON to normalize: ON COALESCE(a.key,-1)=COALESCE(b.key,-1). **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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