ISNULL Function in SQL

ISNULL is a function used to replace NULL values with a specified replacement value.

Purpose

• When a column or expression returns NULL, ISNULL lets you substitute it with a default value.

• Helps avoid NULL results in queries.

Syntax (SQL Server):

ISNULL(expression, replacement_value)

• expression: The value to check for NULL.

• replacement_value: The value to return if expression is NULL.

Example:

SELECT ISNULL(phone, 'No Phone') AS phone_numberFROM employees;

• If phone is NULL, it will display 'No Phone'.

Notes:

• In MySQL, the equivalent is IFNULL().

• In Oracle, use NVL().

• ISNULL is mainly used in SQL Server and Sybase.

If you want examples in other databases or how to use it in queries, just ask!