use warnings;
use strict;

my $onlyUse = 0;
my @unitRow;
my $csr2 = bless {count => 0};
my %seen;

while (my @unitRow = $csr2->fetchrow) {
    my $unit = $unitRow[1];
    unless ($seen{$unit}) {
        $seen{$unit}++;
        $onlyUse++;
        print " $onlyUse ";
        next;
    }
}

sub fetchrow {
    my $self = shift;

    return () if $self->{count} > 20;
    return (0, ++$self->{count});
}

##</code><code>##

 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21