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Write a query to identify duplicate customer entries based on email and phone number.

SQLmedium0.4 min readPremium
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Asked at 1 company
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487
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1,863
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Swiggy
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Expert AnswerPremium
72 wordsInterview-ready
SELECT email, phone_number, COUNT(*) AS duplicate_count FROM customers GROUP BY email, phone_number HAVING COUNT(*) > 1. To list rows: SELECT c.* FROM customers c JOIN (SELECT email, phone_number FROM customers GROUP BY email, phone_number HAVING COUNT(*) > 1) dup ON c.email = dup.email AND c.phone_number = dup.phone_number. **Why**: Normalize email (lower, trim) and phone (strip formatting) before comparison. **Scalability**: Use COALESCE for NULLs in composite keys....
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