mysql_close closes the non-persistent connection to the MySQL server that's associated with the specified link identifier. If link_identifier isn't specified, the last opened link is used.
Open non-persistent MySQL connections and result sets are automatically destroyed when a PHP script finishes its execution. So, while explicitly closing open connections and freeing result sets is optional, doing so is recommended. This will immediately return resources to PHP and MySQL, which can improve performance. For related information, see freeing resources
The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect is assumed. If no connection is found or established, an E_WARNING level error is generated.
Returns true on success or false on failure.
mysql_close will not close persistent links created by mysql_pconnect. For additional details, see the manual page on persistent connections.