Usage of isnull in sql

The ISNULL function in SQL checks whether a value is NULL and returns the specified value (if the value is NULL) or the original value (if the value is non-NULL). Its syntax is: ISNULL(expression, replacement_value). This function is used to replace NULL values ​​to improve readability, prevent errors, and handle NULL values ​​in aggregate functions.

Usage of ISNULL function in SQL

What is the ISNULL function?

The ISNULL function is a SQL function that checks whether a value is NULL and returns a specified value if the value is NULL or the original value if the value is non-NULL.

Syntax:

ISNULL(expression, replacement_value)

Among them:

• expression: The value to check.
• replacement_value: The value returned if expression is NULL.

Usage:

The ISNULL function can be used in various situations, for example:

• Replace the NULL value with a more friendly value , to improve data readability.
• Prevent null values ​​from causing errors or unexpected results.
• Handle NULL values ​​in aggregate functions (such as SUM, COUNT).

Example:

Consider the following table:

##2NULL

ID	Name
1	John Smith

To replace NULL values ​​in the

Name column, you can use the following query:

SELECT ID, ISNULL(Name, 'Unknown') FROM TableName;

Output:

ID#Name1John Smith2Unknown

Note:

The first of the ISNULL function Each parameter must be an expression, not a subquery.
• If
• replacement_value is NULL, the ISNULL function returns the expression itself without replacement.
The ISNULL function is similar to the COALESCE function, but the COALESCE function can accept multiple replacement_values.

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