What is the difference between COUNT(*) and COUNT(column_name)?

Short answer: COUNT(*): Counts all rows, including rows with NULL values in any column. COUNT(column_name): Counts only non-NULL values in the specified column.

Example code

SELECT COUNT(*) FROM employees; -- Counts all rows SELECT COUNT(salary) FROM employees; -- Counts rows where salary is NOT NULL

Real-world example (ShopNest)

ShopNest’s SQL Server database stores customers, products, and orders. Good indexes and clear foreign keys keep checkout queries fast and safe.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.