$sth = $dbh->prepare("INSERT INTO walstock (sid, name, qty) VALUES (?,?,?)");
# ok, we have 3 placeholders, pass 3 params to the execute function.

if ($sth->execute('DEFAULT', $Data1, $Data2)) {
  print "Worked, cool";
}
else {
  print "Didn't work, uncool, error is: $DBI::errstr";
}