What is the return value of Access SQL Max function?

Hi I use Visual C++ MFC 4.2.

I need to get the last support_code from the table so I make query like this:
    CString sSQL;
    sSQL.Format( "SELECT MAX( support_no ) AS \"last\" FROM history WHERE
support_no LIKE \'%s*\'", sYear );

I have tested it in the MS Access and it worked fine. It should return
Support Code in the form like this: "S08-00012" so it has S and - characters
inside.

Now. the problem is from the programming side.

    rs.Open( CRecordset::forwardOnly, ( sSQL ) );

    CString sSupportNo;
    CString sNextCounter;

    if( !rs.IsEOF() ){
        rs.GetFieldValue( "last", varSupportNo );
        ASSERT( varSupportNo.m_dwType == DBVT_STRING );

        sSupportNo = *varSupportNo.m_pstring;
    }

The error is at the ASSERT part. I know the error but I don't know how to
fix it.
The point is that the value of field "last" is not a CString. I don't know
what it is, because I also have tried DOUBLE type it neither work.

What is the return value of the MAX here?

Thank you very much.