what i'd personally do is run a high tensity script doing all the work in php.
PHP Code:
$users = U_QUERY;
while ($all_users = $db->fetch_array(U_QUERY))
{
$current_users[] = $all_users['userid'];
}
$journals = J_QUERY;
while ($all_journals = $db->fetch_array(J_USERS))
{
if (!in_array($all_journals['userid'], $current_users))
{
$journals_to_be_deleted = $all_journals['userid'] . ", ";
}
}
// do delete query here
something like that