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 ifexpressionis 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:

Namecolumn, you can use the following query:

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

Note:

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

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