Name:     IP1:      IP2:
asdf      1.1.1.1   2.2.2.2
Horst     3.3.3.3   4.4.4.4

 print length("String");

while(my @row = $sth->fetchrow_array())
{
	if( $max0 < length($row[0]) ) { $max0=length($row[0]) }
	if( $max1 < length($row[1]) ) { $max1=length($row[1]) }
	if( $max2 < length($row[2]) ) { $max2=length($row[2]) }	
}

SELECT max(Spalte) as maximum FROM Tabelle GROUP BY Spalte

my $stmt = "SELECT MAX(CHAR_LENGTH(spalte1)), MAX(CHAR_LENGTH(spalte2)), MAX(CHAR_LENGTH(spalte3)) FROM tabelle";
my $sth = $dbh->prepare( $stmt ) or die $dbh->errstr;
$sth->execute or die $dbh->errstr;

my ($max_row1, $max_row2, $max_row3) = $sth->fetchrow_array;