mysql_select_db

Function name: mysql_select_db()

Applicable version: PHP 5.x - PHP 7.x (deprecated)

Function Description: The mysql_select_db() function is used to select a MySQL database so that subsequent database operations are performed in the database.

Syntax: bool mysql_select_db ( string $database_name [, resource $link_identifier = NULL ] )

parameter:

• $database_name: The database name to select.
• $link_identifier (optional): Database connection identifier. If this parameter is not provided, the most recently opened database connection is used by default.

Return value: Return true on success, and false on failure.

Example:

1. Connect to the MySQL database and select the database:

 $link = mysql_connect('localhost', 'username', 'password'); if (!$link) { die('连接数据库失败：' . mysql_error()); } $db_selected = mysql_select_db('database_name', $link); if (!$db_selected) { die('选择数据库失败：' . mysql_error()); } echo '成功选择数据库！';

2. Use the default connection when selecting a database:

 $db_selected = mysql_select_db('database_name'); if (!$db_selected) { die('选择数据库失败：' . mysql_error()); } echo '成功选择数据库！';

Notes:

1. The mysql_select_db() function has been deprecated and is not recommended for use in new projects. It is recommended to use mysqli or PDO extensions for database operations.
2. Before using the mysql_select_db() function, you must first establish a database connection using the mysql_connect() or mysql_pconnect() function.
3. After selecting a database using the mysql_select_db() function, subsequent database operations will be performed in that database until another database is selected or the connection is closed.
4. If the database selection fails, you can use the mysql_error() function to obtain error information for debugging.
5. In PHP 7.x version, the mysql_select_db() function has been removed and the database operation should be performed using the corresponding functions in the mysqli or PDO extension instead.