How to close MySQL connection in PHP

When developing PHP and MySQL, connecting to the database is essential. But a common problem is how to effectively close the database connection to avoid resource waste and security risks. This article will explain how to close a MySQL connection in PHP.

MySQL is a commonly used relational database management system. The MySQL database can be accessed through the MySQL extension of PHP. In PHP, you can use the mysql_connect function to establish a connection to the database as follows:

$link = mysql_connect('localhost', 'user', 'password');

In this example, we connected to a MySQL database named "localhost" and used the username "user" and password "password" for authentication. Once the connection is established, we can execute query statements, update data and other operations. However, after completing these operations, we need to close the connection to release the resources related to the database.

In PHP, there are two ways to close the MySQL connection. The first method is to use the mysql_close function, as shown below:

mysql_close($link);

This function will close the specified connection and release the memory and resources related to it. Note that if the connection is not closed and reconnected, the same resource connection will be used. Therefore, you should try to close the connection immediately after use to avoid resource leaks and security issues.

The second method is to use PHP's garbage collection mechanism. PHP's garbage collection mechanism automatically reclaims unused memory and resources at the end of code execution. You can use this to close the MySQL connection if you want to make sure your PHP code doesn't stutter or stop unexpectedly while running.

When using the garbage collection mechanism, you should make sure to set the mysql resource variable to null. This will notify the PHP garbage collection mechanism to release the resources related to it, as shown below:

$link = mysql_connect('localhost', 'user', 'password');
// 做一些查询和更新操作
$link = null;

This code snippet Set the mysql resource variable to null after completing the operation, so that the PHP garbage collection mechanism will automatically close the connection and release memory and resources after the code is executed.

It should be noted that when using the garbage collection mechanism to close the connection, you must ensure that no other variables refer to this resource, otherwise the garbage collection mechanism will not be able to reclaim the resource. Therefore, before setting a mysql resource variable to null, you should check all variables referencing this resource to ensure that they no longer require a connection to the database.

In short, in PHP applications, closing the MySQL connection is very important. In addition to freeing up memory and resources, it also protects applications from security threats. In this article, we introduced two methods of closing a MySQL connection: using the mysql_close function and using PHP's garbage collection mechanism. No matter which method is used, the connection should be closed promptly after using the database to avoid resource and security issues.

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