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.
Using mysql_close() isn't usually necessary, as non-persistent open links are automatically closed at the end of the script's execution. See also freeing resources.
The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If by chance no connection is found or established, an E_WARNING level warning is generated.
Note: mysql_close() will not close persistent links created by mysql_pconnect().