1 Primary Key - Another not unique

I have a customer file that I import to project each month . I am now using 9.8 and in the future 10.0 which should check for existing records and either update or add new records according to the manual if using a primary key in file. My older project was 9.7 I just truncated table and uploaded a new Customer file, Which I do not want to do anymore due to google map fields which I have to do geocoding every time I import a new file. So I made CustomerID the primary key instead of auto_number . Fine. Only problem is there are several CustomerID's that have EmployeesID's connected to the same Customer ( hence 3 records of CustomerID ) so it can't be the primary key. So I want to use a second key EmployeeID / or non unique field in the table mysql to import . My table looks something like this

CustomerID
EmployeeID
Employee
Division
fldgroup
address
city
state
zip
lat
lng
map

Is it possible to have a primary key and a non-unique composite key in mysql table / project - upon the import . I tried this link with constraint with multiple fields, but I keep getting syntax error in query wizard in my project. If I could use two fields it would make the record unique.

Or do I have to import a file like this
CustomerID
EmployeeID1
EmployeeID2
EmployeeID3

which I am trying to avoid due to numerous Session calls of just the one field called EmployeeID (connections and events) in other tables in the project.

Thanks for any ideas in advance.