use strict;
use DBI;

my $dbh = DBI->connect(
   "DBI:CSV:f_dir=.;csv_eol=\n;csv_sep_char=!;",
   {RaiseError=>1},
);

$dbh->{csv_tables}->{'class'} = { 
   file      => 'class.csv',
   col_names => [qw(id name class instructor)],
};

my $sth = $dbh->selectcol_arrayref("
   select distinct instructor
   from class
");

print join("\n",@$sth),"\n";