Post #2483

✅SQL Functions Interview Questions with Answers🎯📚 1️⃣ Q: What is the difference between COUNT(*) and COUNT(column_name)? A: - COUNT(*) counts all rows, including those with NULLs. - COUNT(column_name) counts only rows where the column is NOT NULL. 2️⃣ Q: When would you use GROUP BY with aggregate functions? A: Use GROUP BY when you want to apply aggregate functions per group (e.g., department-wise total salary): SELECT department, SUM(salary) FROM employees GROUP BY department; 3️⃣ Q: What does the COALESCE() function do? A: COALESCE() returns the first non-null value from the list of arguments. Example: SELECT COALESCE(phone, 'N/A') FROM users; 4️⃣ Q: How does the CASE statement work in SQL? A: CASE is used for conditional logic inside queries. Example: SELECT name, CASE WHEN score >= 90 THEN 'A' WHEN score >= 75 THEN 'B' ELSE 'C' END AS grade FROM students; 5️⃣ Q: What’s the use of SUBSTRING() function? A: It extracts a part of a string. Example: SELECT SUBSTRING('DataScience', 1, 4); -- Output: Data 6️⃣ Q: What’s the output of LENGTH('SQL')? A: It returns the length of the string: 3 7️⃣ Q: How do you find the number of days between two dates? A: Use DATEDIFF(end_date, start_date) Example: SELECT DATEDIFF('2026-01-10', '2026-01-05'); -- Output: 5 8️⃣ Q: What does ROUND() do in SQL? A: It rounds a number to the specified decimal places. Example: SELECT ROUND(3.456, 2); -- Output: 3.46 💡Pro Tip: Always mention real use cases when answering — it shows practical understanding. 💬Tap ❤️ for more!