Context: CREATE TABLE Ref_document_types (document_type_name VARCHAR, document_type_code VARCHAR); CREATE TABLE All_documents (document_type_code VARCHAR, document_name VARCHAR)
Question: What is the document type name for the document with name "How to read a book"?
Answer: 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"