SQL

Im getting a syntax error in my query expression. Can anyone see what Im doing wrong?

SELECT DISTINCT C.CUSTOMER_NUM, C.CUSTOMER_NAME FROM CUSTOMER AS C INNER JOIN ORDERS AS O ON O.CUSTOMER_NUM = C.CUSTOMER_NUM INNER JOIN ORDER_LINE AS OLON OL.ORDER_NUM = O.ORDER_NUM INNER JOIN ITEM AS I ON I.ITEM_NUM - OL.ITEM_NUM WHERE I.DESCRIPTION = 'ROCKING HORSE';