CREATE TABLE employees (employee_id NUMBER, role_code CLOB, employee_name CLOB, other_details CLOB)
CREATE TABLE documents_mailed (document_id NUMBER, mailed_to_address_id NUMBER, mailing_date TIME)
CREATE TABLE ref_document_status (document_status_code CLOB, document_status_description CLOB)
CREATE TABLE addresses (address_id NUMBER, address_details CLOB)
CREATE TABLE documents (document_id NUMBER, document_status_code CLOB, document_type_code CLOB, shipping_agent_code CLOB, receipt_date TIME, receipt_number CLOB, other_details CLOB)
CREATE TABLE circulation_history (document_id NUMBER, draft_number NUMBER, copy_number NUMBER, employee_id NUMBER)
CREATE TABLE ref_document_types (document_type_code CLOB, document_type_description CLOB)
CREATE TABLE roles (role_code CLOB, role_description CLOB)
CREATE TABLE draft_copies (document_id NUMBER, draft_number NUMBER, copy_number NUMBER)
CREATE TABLE document_drafts (document_id NUMBER, draft_number NUMBER, draft_details CLOB)
CREATE TABLE ref_shipping_agents (shipping_agent_code CLOB, shipping_agent_name CLOB, shipping_agent_description CLOB)

For each document, list the number of employees who have showed up in the circulation history of that document. List the document ids and number of employees.
SELECT document_id, COUNT(DISTINCT employee_id) FROM circulation_history GROUP BY document_id
SELECT "document_id", COUNT(DISTINCT "employee_id") FROM "circulation_history" GROUP BY "document_id"