SELECT M.msg_id, 
       SND.firstname as snd_fname, SND.lastname as snd_lname,
       REC.firstname as rec_fname, REC.lastname as rec_lname
from MSG as M
-- We'll use SND as the alias for the sender
join USERS as SND on M.msg_from = SND.usrid
-- and REC as the alias for the recipient
join USERS as REC on M.msg_to   = REC.usrid

##</code><code>##

$data->execute();
my $data_check = $data->fetchall_arrayref();
for my $row (@$data_check) {
   my ($msgid, $snd_fname, $snd_lname, $rec_fname, $rec_lname) = @$row;
   printf "% 6u %-32.32s %-32.32s\n", 
         $msgid, 
         join(" ", $snd_lname, $snd_fname), 
         join(" ", $rec_lname, $rec_fname);
}

##</code><code>##

$data->execute();
my $data_check = $data->fetchall_arrayref();
while (my $row = $data->fetchrow_hashref) {
   printf "% 6u %-32.32s %-32.32s\n", 
         $row->{msgid}, 
         join(" ", $row->{snd_lname}, $row->{snd_fname}), 
         join(" ", $row->{rec_lname}, $row->{rec_fname});
}