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 Project_Staff (date_from VARCHAR, date_to VARCHAR, role_code VARCHAR)
### Question:
When do all the researcher role staff start to work, and when do they stop working?
### Answer:
SELECT date_from, date_to FROM Project_Staff WHERE role_code = 'researcher'