DBSUM ALL|SELECTED|UNSELECTED %FieldName ResVar

  This command is for DataBase listviews.

  It will add the fields of ALL or the SELECTED or the UNSELECTED
  records of the listview and place the result into ResVar.
  
  ex:

  ; use a listview and go to the 1st record
  lvuse mygui 1
  lvgo first
  ; hide the listview for speed..
  setgad mygui 1 HIDE
  ; unselect all records that may have been selected
  lvmulti NONE
  ; go through all records, selecting all for which the field "%amount"
  ; is over 1000
  while $$lv.line > ''
     if $%amount > 1000
        lvmulti ON
     endif
     lvgo next
  endwhile 
  ; sum all selected records
  dbsum SELECTED %amount result
  ; print the result
  say 'The total of all amounts over 1000 is : $resultn'
  ; set the listview back on
  setgad mygui 1 SHOW