SELECT SUM(itm.item_cash_staked - itm.item_cash_won)
FROM item itm
WHERE itm.item_rejection_code_id IS null
  AND itm.item_created_on > '2019-08-01 17:38:33.613+01'
  AND EXISTS (select *
              from product p
              where p.product_id = itm.product_id
                and p.customer_id = 123456)