How to close database connection using PHP

PHP is a popular server-side scripting language that has been widely used for web development. PHP's database extensions (or drivers) enable developers to use various database systems, such as MySQL, Oracle, SQL Server, etc. When using PHP for database programming, closing the database connection is an important task.

In this article, we will discuss how to close a database connection using PHP.

1. Why should we close the database connection?

In PHP, connecting to the database consumes server resources. Therefore, it's a good idea to close the database connection whenever you're done accessing data. This frees up server resources, improving application performance and scalability. Additionally, since the database connection is over a network connection, closing it frees up network ports so that other machines can use them.

2. How to close the database connection?

In PHP, there are two ways to close a database connection: using the mysqli_close() function and using the close() method of the PDO (PHP Data Object) class.

The following is an example of using the mysqli_close() function to close the database connection:

//连接到MySQL数据库
$conn = mysqli_connect("localhost", "my_user", "my_password", "my_db");

//执行查询操作
$result = mysqli_query($conn, "SELECT * FROM my_table");

//关闭数据库连接
mysqli_close($conn);

As shown above, we use the mysqli_connect() function to connect to the MySQL database, and then use the mysqli_query() function to perform query operations . Finally, we close the database connection using the mysqli_close() function.

It is easier to close the database connection using the PDO class:

//连接到MySQL数据库
$conn = new PDO('mysql:host=localhost;dbname=my_db', 'my_user', 'my_password');

//执行查询操作
$stmt = $conn->query('SELECT * FROM my_table');

//关闭数据库连接
$conn = null;

Here, we use the PDO::query() method to perform the query operation, and use $conn = null; to close the database connection.

Please note that after closing the database connection, any attempt to access the database will fail.

3. Closing the database connection time

In web applications, the time to close the database connection is very important. If you open and close connections at the beginning or end of your script, then when the script is busy, each page request will cause a database connection to be opened and closed, which can severely impact the performance of your application. Therefore, a better approach is to close the connection only when it needs to be closed.

For example, you can open and close the database connection in the body of the script instead of opening and closing it in a function or include file:

//脚本主体
function myFunction() {
    //连接到MySQL数据库
    $conn = new PDO('mysql:host=localhost;dbname=my_db', 'my_user', 'my_password');

    //执行查询操作
    $stmt = $conn->query('SELECT * FROM my_table');

    //关闭数据库连接
    $conn = null;
}

//调用函数
myFunction();

As shown above, we have myFunction() Open and close database connections in the body of the function. This will only connect to the database when the function is called, which will reduce the number of times the database connection is opened and closed.

4. Conclusion

When dealing with databases in PHP, closing the database connection is an essential task. Closing database connections frees up server resources, improving application performance and scalability. In this article, we discussed how to close database connections using mysqli_close() function and close() method of PDO class and when to close them. When writing PHP applications, remember to close database connections for optimal performance and scalability.

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