How does SQL Server handle NULL values in comparisons?

Hi Sandhiya Priya,

In SQL Server, NULL represents unknown or missing value. It behaves differently in comparisons than regular values.

Comparison with NULL using operators such as =, <>, <, >, etc. will returns UNKNOWN. It will not return TRUE or FALSE.

SELECT CASE WHEN NULL = NULL THEN 'True' ELSE 'False' END AS Result;

Output: 

• False

Using IS NULL and IS NOT NULL is the only reliable ways to test for NULL 

WHERE column IS NULL
WHERE column IS NOT NULL

Hope this will help you!

SQL Server, NULL represents an unknown or missing value, and it behaves differently from regular values.

SELECT * FROM Student WHERE StudentID = NULL;
You might expect it to find rows where StudentID is NULL — but it won’t return anything.
That’s because NULL = NULL is not TRUE; it’s UNKNOWN (since you can’t be sure two unknowns are equal).

So the correct way to check null values is

IS NULL      -- to check if a value is NULL
IS NOT NULL  -- to check if a value is not NULL

Example:
SELECT * FROM Student  WHERE StudentID IS NULL;