while (my $row = $sth->fetchrow_hashref) {
  for my $db (@{$where{NEW_DB}}) {
     $row->{Db} = $db;
     for my $user (@{$where{NEW_USER}}) {
        $row->{User} = $user;
        print "INSERT INTO DB ";
        print join(",", map { "$_:'$row->{$_}'" } keys %{$row});
        print ";\n";
     }
  }
}