Count the number of documents with the type code BK that correspond to each product id.
SELECT count(*) ,  project_id FROM Documents WHERE document_type_code  =  "BK" GROUP BY project_id
SELECT count(*) ,  project_id FROM Documents WHERE document_type_code  =  "BK" GROUP BY project_id
[{'count(*)': 2, 'Project_ID': 30}, {'count(*)': 1, 'Project_ID': 35}, {'count(*)': 3, 'Project_ID': 105}]