这是PHP手册中的一段关于mysql_connect的说明：
If a second call is made to mysql_connect() with the same arguments, no new link will be established, but instead, the link identifier of the already opened link will be returned. The new_link parameter modifies this behavior and makes mysql_connect() always open a new link, even if mysql_connect() was called before with the same parameters. The client_flags parameter can be a combination of the constants MYSQL_CLIENT_SSL, MYSQL_CLIENT_COMPRESS, MYSQL_CLIENT_IGNORE_SPACE or MYSQL_CLIENT_INTERACTIVE. 注: The new_link parameter became available in PHP 4.2.0 The client_flags parameter became available in PHP 4.3.0 The link to the server will be closed as soon as the execution of the script ends, unless it's closed earlier by explicitly calling mysql_close().
If a second call is made to mysql_connect() with the same arguments, no new link will be established, but instead, the link identifier of the already opened link will be returned. The new_link parameter modifies this behavior and makes mysql_connect() always open a new link, even if mysql_connect() was called before with the same parameters. The client_flags parameter can be a combination of the constants MYSQL_CLIENT_SSL, MYSQL_CLIENT_COMPRESS, MYSQL_CLIENT_IGNORE_SPACE or MYSQL_CLIENT_INTERACTIVE. 注: The new_link parameter became available in PHP 4.2.0 The client_flags parameter became available in PHP 4.3.0 The link to the server will be closed as soon as the execution of the script ends, unless it's closed earlier by explicitly calling mysql_close().
mysql_pcconnect
或
odbc_pcconnect
mssql_pcconnect
....