# Assume that %file has the filename for each field in your
# table and @fields has the list of field names.
my @fhs;
for my $field (@fields) {
  open(my $fh, "<", $file{$field})
    or die "Can't open '$file{$field}: $!";
  push @fhs, $fh;
}

while (1) {
  my $did_read;
  my @data;
  for my $fh (@fhs) {
    my $rec = <$fh>;
    if (defined($rec)) {
      $did_read++;
      push @data, $rec;
    }
    else {
      push @data, "";
    }
  }

  if ($did_read) {
    insert_data(@data);
  }
  else {
    # Came to the end of all data streams
    last;
  }
}