/* SUM and AVERAGE via PP rule. */

PROCEDURE Main()
   LOCAL aStruct, nSum, nAvg

   FErase( "people.dbf" )
   aStruct := { { "ID", "N", 4, 0 }, { "AGE", "N", 3, 0 } }
   dbCreate( "people.dbf", aStruct )
   USE people.dbf NEW EXCLUSIVE ALIAS p
   dbAppend() ; FieldPut(1, 1) ; FieldPut(2, 18)
   dbAppend() ; FieldPut(1, 2) ; FieldPut(2, 25)
   dbAppend() ; FieldPut(1, 3) ; FieldPut(2, 30)
   dbAppend() ; FieldPut(1, 4) ; FieldPut(2, 45)
   dbAppend() ; FieldPut(1, 5) ; FieldPut(2, 60)
   dbCommit()

   /* SUM all ages */
   dbGoTop()
   SUM p->age TO nSum
   ? "1. SUM p->age =", nSum, "(expect 178 = 18+25+30+45+60)"

   /* SUM with FOR */
   dbGoTop()
   SUM p->age TO nSum FOR p->age >= 30
   ? "2. SUM p->age FOR age>=30 =", nSum, "(expect 135 = 30+45+60)"

   /* AVERAGE all ages */
   dbGoTop()
   AVERAGE p->age TO nAvg
   ? "3. AVERAGE p->age =", nAvg, "(expect 35.6)"

   /* AVERAGE with FOR */
   dbGoTop()
   AVERAGE p->age TO nAvg FOR p->age >= 30
   ? "4. AVERAGE p->age FOR age>=30 =", nAvg, "(expect 45)"

   /* AVERAGE with no matching rows */
   dbGoTop()
   AVERAGE p->age TO nAvg FOR p->age > 200
   ? "5. AVERAGE p->age FOR age>200 =", nAvg, "(expect 0)"

   dbCloseArea()
   FErase( "people.dbf" )
   ? "DONE"
   RETURN