SELECT
  statistics.borrowernumber AS BorrowerNumber,
  sum(items.replacementprice) AS AmountSavedUsingLibrary
FROM
  statistics
INNER JOIN items USING (itemnumber)
WHERE
  date(statistics.datetime) BETWEEN <<Checked out BETWEEN (yyyy-mm-dd)|date>> AND <<and (yyyy-mm-dd)|date>>
  AND statistics.type = 'issue'
GROUP BY statistics.borrowernumber
ORDER BY AmountSavedUsingLibrary DESC