use DBI;

DBI connection stuff here...

# no error handling code included in this sample

$sth = $dbh->prepare(qq|SELECT row_id FROM test WHERE exe='N'|);
$rows = $sth->execute(); 

$sth2 = $dhb->prepare(qq|UPDATE test SET exe = 'Y' WHERE row_id = ?|);

while ($row_id = $sth->fetchrow_array()) {
    # now execute the 2nd statement replacing the 
    # placeholder with the variable $row_id
    $sth2->execute($row_id); 
    }
$sth->finish();
$sth2->finish();
$dbh->disconnect();