What is NULL in SQL and how is it handled?

Short answer: NULL represents the absence of a value in a column. It is not the same as an empty string or zero. Handling NULL: To check for NULL, use IS NULL or IS NOT NULL. To handle NULL in queries, use COALESCE() (returns the first non-NULL value) or IFNULL().

Example code

SELECT Name, IFNULL(Salary, 0) FROM Employees;

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.