Usage of ifnull in mysql

IFNULL function is used to check whether the expression is NULL. If so, it returns the specified default value, otherwise it returns the expression. Available scenarios include: preventing NULL values ​​from causing errors, converting NULL values ​​into meaningful values, and using default values ​​to handle NULL values ​​in aggregate functions.

Usage of IFNULL function in MySQL

The IFNULL function is a very useful MySQL function that is used for Checks whether the given expression is a NULL value and returns a specified default value if it is NULL, otherwise returns the given expression.

Syntax

<code>IFNULL(expression, default_value)</code>

Where:

• expression is an expression to be checked for NULL.
• default_value is the default value to be returned if expression is NULL.

Usage

The IFNULL function is useful in the following situations:

• Prevent NULL values ​​from causing errors in query results.
• Convert NULL values ​​to meaningful values.
• Use default values ​​in aggregate functions to handle NULL values.

Example

The following example shows how to use the IFNULL function to prevent NULL values ​​from causing errors in query results:

SELECT username, IFNULL(email, 'N/A') AS email
FROM users;

If the table If the email field of a user is NULL, the query results will be as follows:

<code>+---------+-------+
| username | email  |
+---------+-------+
| John     | john@example.com |
| Mary     | mary@example.com |
| Peter    | N/A    |
+---------+-------+</code>

By using the IFNULL function, we avoid errors due to NULL values ​​and replace them with a meaningful default value ( In this case "N/A").

Note

• If default_value is NULL, the IFNULL function will return expression itself (if expression is not NULL).
• IFNULL function can only return scalar values. It cannot be used to return collection or table values.

The above is the detailed content of Usage of ifnull in mysql. For more information, please follow other related articles on the PHP Chinese website!