Duplicate Detection

How can we identify duplicate email addresses in a customer database?

Advanced⏱ 3 Minutes⭐ 1830 XP

🤔 THE QUESTION

How can we identify duplicate email addresses in a customer database?

💡 WHAT IS IT?

Grouping by candidate key fields and filtering for HAVING COUNT(*) > 1 pinpoints duplicates.

🎯 WHAT IS IT USED FOR?

Data quality checks, primary key collision audits, fraud detection.

💻 EXAMPLE

SELECT
email,
COUNT(*) AS duplicate_count
FROM customers
GROUP BY email
HAVING COUNT(*) > 1;

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