Task: Text to Code
Input (English): SQL: SELECT Count ( * ) FROM Ref_Document_Types
Feedback: Replace reference document types table with documents table and Make sure shipping agent name equals USPS for document id .
Output (English): SELECT count(*) FROM Ref_Shipping_Agents JOIN Documents ON Documents.shipping_agent_code = Ref_Shipping_Agents.shipping_agent_code WHERE Ref_Shipping_Agents.shipping_agent_name = "USPS"