UPDATE ... WHERE writing a new line

[Paul A]

I am having trouble converting valid MySQL command line to Perl. This works:

mysql> UPDATE control_number SET ctrlnum=714568 WHERE id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

mysql> SELECT * FROM control_number;
+---------+------+
| ctrlnum | id |
+---------+------+
| 714568 | 1 |
+---------+------+

But when I run it in a production .pl (increment by 1 every time the script is called), it writes a new line:

my $sth = $dbh->prepare("UPDATE control_number SET ctrlnum='$max' WHERE id = 1;");
$sth->execute;
+---------+------+
| ctrlnum | id |
+---------+------+
| 714568 | 1 |
| 714569 | NULL |
+---------+------+

Cane somebody please help? Many thanks. -- Paul