What document types have more than 2 corresponding documents?
SELECT document_type_code FROM documents GROUP BY document_type_code HAVING count(*)  >  2
SELECT document_type_code FROM documents GROUP BY document_type_code HAVING count(*)  >  2
[{'document_type_code': 'Advertisement'}, {'document_type_code': 'Book'}, {'document_type_code': 'CV'}, {'document_type_code': 'Paper'}]