Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE Circulation_History (document_id VARCHAR, employee_id VARCHAR)
### Question:
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.
### Answer:
SELECT document_id, COUNT(DISTINCT employee_id) FROM Circulation_History GROUP BY document_id