Someday, you may need problem that must connect to more than one kind database. Example, staffing database in oracle and finance in mysql. You must collaborate 2 database in one application.
<?php
include('adodb.inc.php');
# load code common to ADOdb
$conn1 = &ADONewConnection('mysql');
# create a mysql connection
$conn2 = &ADONewConnection('oracle');
# create a oracle connection
$conn1->PConnect($server, $userid, $password, $database);
$conn2->PConnect(false, $ora_userid, $ora_pwd, $oraname);
$conn1->Execute('insert ...');
$conn2->Execute('update ...');
?>