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The ISNULL() function
4. The ISNULL() function
The COALESCE() function
The NULLIF() function


Now we will learn a useful SQL Server function: ISNULL(). It replaces NULL with a given value, and it looks like this:

ISNULL(expression, replacement)

It takes two arguments:

  • expression is where SQL will look for NULLs.This argument can be a string, column name, or any other expression.
  • replacement is what you want to replace all the NULLs in the expression with.

Study the example below:

  ISNULL(Type, N'unknown') AS Type
FROM Product;

This query searches the Type column in the Product table for NULLs. When it finds one, it replaces it with N'unknown'.

Ready to practice?


Some products haven't been assigned a category. Select each product's name and category from the Product table. Name the second column Category, and put a N'---' string wherever there is a NULL.

Stuck? Here's a hint!

Use ISNULL() with the Category column and a N'---' string.