Post #2617

📊Interviewer: How do you remove duplicate records in SQL? 👋Me: We can remove duplicates using DISTINCT, GROUP BY, or delete duplicate rows using ROW_NUMBER(). ✅1️⃣ Using DISTINCT (to fetch unique values) SELECT DISTINCT column_name FROM employees; 👉 Returns unique records but does not delete duplicates. ✅2️⃣ Using GROUP BY (to identify duplicates) SELECT name, COUNT(*) FROM employees GROUP BY name HAVING COUNT(*) > 1; 👉 Helps find duplicate records. ✅3️⃣ Delete Duplicates Using ROW_NUMBER() (Most Important ⭐) (Keeps one record and deletes others) DELETE FROM employees WHERE id IN ( SELECT id FROM ( SELECT id, ROW_NUMBER() OVER ( PARTITION BY name, salary ORDER BY id ) AS rn FROM employees ) t WHERE rn > 1 ); 🧠Logic Breakdown: - DISTINCT → shows unique records - GROUP BY → identifies duplicates - ROW_NUMBER() → removes duplicates safely ✅Use Case: Data cleaning, ETL processes, data quality checks. 💡Tip: Always take a backup before deleting duplicate records. 💬Tap ❤️ for more!