A question mark result from ExecuteSQL indicates a SQL syntax error in most cases. In other cases, it just means that your field is too narrow to display the data returned by your calculation.
So you'll need to check the details of your query and also try clicking into the field while in Browse mode. (If field is too narrow, you'll see the results when you click into the field.) I don't see any obvious syntax errors so you may need to double check field names. (I don't think any need quotes but you can also try enclosing the field names in quotes.)
I have tried this both unqualified (as above) and qualified (PeopleRole::Consultant_certification_achieved).
The correct syntax for a qualified field reference in SQL is PeopleRole.Consultant_certification_achieved.