Where is mysql_close() used?

mysql_close() is used to close the connection with the MySQL database server. Usage: First establish a connection with the MySQL database server through the "mysql_connect()" function, and store the connection identifier in the $conn variable. Then, you can perform database operations, such as querying data, inserting data, etc., and finally, by calling The "mysql_close()" function closes the database connection and releases resources.

The operating environment of this article: Windows 10 system, MySQL version 8.0.32, Dell g3 computer.

MySQL database is a commonly used relational database management system, and mysql_close() is one of the MySQL database connection functions. This article will introduce in detail the function and usage of the mysql_close() function.

MySQL database connection refers to establishing a connection with the MySQL database server in PHP code so that you can send SQL statements to the database server and obtain results. In PHP, we can use the mysql_connect() function to establish a connection to the MySQL database. After connecting to the database, we can perform various operations, such as querying data, inserting data, updating data, deleting data, etc.

Corresponding to the mysql_connect() function that establishes a database connection is the mysql_close() function, which is used to close the connection with the MySQL database server. In actual applications, when we complete the interaction with the database, we should immediately close the database connection and release resources. This can effectively reduce the load on the server and prevent performance problems when there are too many clients connected to the database server. Therefore, the mysql_close() function is very important.

The syntax of the mysql_close() function is very simple, just specify the connection identifier to be closed. The syntax is as follows:

mysql_close ( resource $connection_identifier = ? ) : void

In the function, the $connection_identifier parameter is optional and represents the MySQL database connection identifier to be closed. If this parameter is not specified, the function attempts to close the previously opened connection. Of course, this is not a recommended approach, because in the case of multiple database connections, not knowing which connection to close may lead to unexpected errors, so it is best to store the connection identifier in a variable when calling the mysql_connect() function , and specify the specific connection identifier when calling the mysql_close() function.

The following is an example to illustrate the use of the mysql_close() function:

$conn = mysql_connect("localhost", "root", "password"); // 建立数据库连接
// 执行数据库操作
// 关闭数据库连接
mysql_close($conn);

In the above example, we first establish a connection with the MySQL database server through the mysql_connect() function, and then The connection identifier is stored in the $conn variable. Subsequently, we can perform database operations such as querying data, inserting data, etc. Finally, close the database connection and release resources by calling the mysql_close() function.

It should be noted that after PHP 5.5.0 version, the mysql_close() function has been deprecated. This is because PHP officially recommends using mysqli or PDO to connect to the database, not the mysql extension. Therefore, in new PHP projects, we should use the corresponding closing method provided by mysqli or PDO to replace the mysql_close() function.

In short, the mysql_close() function plays a very important role in MySQL database connection. It can release resources in time, reduce the burden on the server, and improve application performance. For old PHP projects, we can continue to use the mysql_close() function, but for new PHP projects, you should use mysqli or PDO to connect to the database and use the corresponding method to close the database connection.

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