* Read the raw data;
DATA flowersales;
   INFILE 'd:\MySASLib\TropicalSales.dat';
   INPUT CustomerID $4. @6 SaleDate MMDDYY10. @17
      Variety $9. Quantity;
PROC SORT DATA = flowersales;
   BY DESCENDING Quantity;

* Find biggest order and pass the customer id to a macro variable;
DATA _NULL_;
   SET flowersales;
   IF _N_ = 1 THEN CALL SYMPUT("selectedcustomer",CustomerID);
   ELSE STOP;

PROC PRINT DATA = flowersales;
   WHERE CustomerID = "&selectedcustomer";
   TITLE "Customer &selectedcustomer Had the Single Largest Order";
RUN;