presto-parser/src/main/java/io/prestosql/sql/tree/QualifiedName.java/QualifiedName/getPrefix
class QualifiedName:    public Optional<QualifiedName> getPrefix()
    {
        if (parts.size() == 1) {
            return Optional.empty();
        }

        List<Identifier> subList = originalParts.subList(0, originalParts.size() - 1);
        return Optional.of(new QualifiedName(subList));
    }