Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE staff_department_assignments ( department_id VARCHAR )

### Question ###
What is the id of the department with the least number of staff?

### Accurate SQL ###

SELECT department_id FROM staff_department_assignments GROUP BY department_id ORDER BY COUNT(*) LIMIT 1