I guess the table doesn't have a primary key? Also you should use RaiseError or else check the status of every DBI statement. Anyway you're probably being redundant by specifying 'where rowid = .. and exe_c = ..'. And you can still use placeholders(psuedocode ahead):

my $dbh = DBI->connect('...', 'user','passwd',
 {PrintError=>0, RaiseError=>1});
my $sql = <<EOT;
select ... from .. where exe_c = 'N'
EOT
my $sel_h = $dbh->prepare($sql);
$sql = <<EOT;
update ... set exe_c = 'N' where rowid = ?
EOT
my $upd_h = $dbh->prepare($sql);
$sel_h->execute;
$sel_h->bind_columns(...);
while ($sel_h->fetch) {
 ...
 $upd_h->execute($rowid);
}
$dbh->disconnect;
[download]

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ooo  O\O  ooo tilly was here :,(