DELETE
FROM
    ITEM
WHERE
    ITEM_CODE IN(
                    SELECT 
                        S.ITEM_CODE
                    FROM 
                        STOCK AS S
                            LEFT OUTER JOIN ITEM AS I
                                ON S.ITEM_CODE = I.ITEM_CODE
                    WHERE 
                        (S.ITEM_CODE NOT IN (SELECT ITEM_CODE FROM ITEM) OR 
                        LAST_DELIVERY_DATE < date('now', '-6 months'))
                        AND 
                        STOCK_MANAGEMENT_TYPE = 1
    );