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 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?

### Accurate SQL ###

SELECT date_from, date_to FROM Project_Staff WHERE role_code = 'researcher'