Show all document names.
select document_name from all_documents
For each of them, show the document type name.
select t2.document_type_name, t1.document_name from all_documents as t1 join ref_document_types as t2 on t1.document_type_code = t2.document_type_code
What is the type name for the document named "How to read a book"?
select t2.document_type_name from all_documents as t1 join ref_document_types as t2 on t1.document_type_code = t2.document_type_code where t1.document_name = "How to read a book"