In this guide, we will discuss the issue of receiving the "Call to Undefined Function mysql_select_db()" error in PHP and provide a step-by-step solution to fix it. This error is commonly encountered when the deprecated mysql_* functions are used in PHP scripts, and it can disrupt your application's functionality. By following this comprehensive guide, you will be better equipped to identify and rectify this issue.
Table of Contents
- Step 1 - Verify PHP Version and MySQL Extension
- Step 2 - Update Deprecated Code
- Step 3 - Test the Updated Code
Understanding the Error
The "Call to Undefined Function mysql_select_db()" error occurs when you are using the deprecated mysql_* functions in your PHP scripts. These functions have been removed as of PHP 7.0, and using them will result in errors. The recommended approach is to use the mysqli_* functions or the PDO (PHP Data Objects) extension for connecting to and interacting with your MySQL databases.
Fixing the Error
To fix the "Call to Undefined Function mysql_select_db()" error, follow the steps below:
Step 1 - Verify PHP Version and MySQL Extension
The first step in fixing the error is to verify your PHP version and the MySQL extension being used. You can do this by creating a PHP file with the following code:
<?php
phpinfo();
?>
Save the file as phpinfo.php and access it through your browser. Look for the PHP version and the MySQL extension (either mysql, mysqli, or pdo_mysql). If your PHP version is 7.0 or higher, you will need to update your code to use the mysqli_* functions or the PDO extension. If the MySQL extension is missing, you can install it by following the installation instructions in the PHP documentation.
Step 2 - Update Deprecated Code
After verifying your PHP version and MySQL extension, you will need to update your code to replace the deprecated mysql_* functions with either the mysqli_* functions or the PDO extension. Here's an example of how to update your code to use the mysqli_* functions:
Deprecated Code (Using mysql_* Functions)
<?php
$connection = mysql_connect('localhost', 'username', 'password');
mysql_select_db('database_name', $connection);
// Your queries and other code here...
?>
Updated Code (Using mysqli_* Functions)
<?php
$connection = mysqli_connect('localhost', 'username', 'password', 'database_name');
// Your queries and other code here...
?>
Step 3 - Test the Updated Code
After updating your code, test it to ensure that the "Call to Undefined Function mysql_select_db()" error has been resolved. Access your application through the browser and verify that the error is no longer occurring. If you still encounter issues, double-check your code for any remaining instances of the deprecated mysql_* functions and update them accordingly.
FAQ
Why am I getting the "Call to Undefined Function mysql_select_db()" error?
This error occurs when you are using the deprecated mysql_* functions in your PHP scripts. These functions have been removed as of PHP 7.0, and using them will result in errors.
What should I use instead of the mysql_* functions?
The recommended approach is to use the mysqli_* functions or the PDO (PHP Data Objects) extension for connecting to and interacting with your MySQL databases.
Is it safe to continue using the mysql_* functions?
No, it is not safe to continue using the mysql_* functions. These functions are deprecated and have been removed as of PHP 7.0, which means they are no longer maintained and may have security vulnerabilities.
How can I tell if my PHP scripts are using the deprecated mysql_* functions?
You can search your PHP scripts for instances of mysql_ to find any occurrences of the deprecated mysql_* functions.
Can I use the mysqli_* functions and the PDO extension together?
Yes, you can use both the mysqli_* functions and the PDO extension in the same PHP script. However, it is recommended to choose one method and use it consistently throughout your application for better code organization and maintainability.