orders表和order_items表的结构如下: orders表: Name Null? Type order_id not null number(4) primary key order_date date customer_id number(3) order_total number(7,2) order_items表: name null? type order_id not null number(12) line_item not null number(3) product_id not null number(6) unit_price number(8,2) quantity number(8) SQL语句:UPDATE orders SET order_date=sysdate WHERE order_id IN (SELECT order_id FROM order_items WHERE quantity IS NULL); 该语句的执行结果是: