my $abstUP = SQL::Abstract->new();

  while( my $row = $sth->fetchrow_hashref() ){
       print "$0 : Processing row: ".Dumper($row)."\n";

       # $subexec is a subref which takes the row as a hashref
       # and returns a modified clone of it to be inserted into the db
       # so, newrow and row have the same keys exactly
       my $newrow = $subexec->($row, $colnames);
       print "$0 : result is: ".Dumper($newrow)."\n";
       my $newrow_only_colnames = { %{ $newrow }{@$colnames} };

       # Update the row
       my($stmt, @bind) = $abstUP->update($tablename, $newrow_only_colnames,
	   { id => $row->{id} } );
       print "executing SQL:\n$stmt\nwith binds:\n@bind\n";
       my $sth_upd = $dbh->prepare($stmt);
       if( ! $sth_upd->execute(@bind) ){
         $dbh->rollback();
         die "update (and rolling back): ".$dbh->errstr;
       }
  }