154. View the Exhibit and evaluate structures of the SALES, PRODUCTS, and COSTS tables.
Evaluate the following SQL statement:
SQL>SELECT prod_id FROM products
INTERSECT
SELECT prod_id FROM sales
MINUS
SELECT prod_id FROM costs;
Which statement is true regarding the above compound query?
A. It produces an error.
B. It shows products that were sold and have a cost recorded.
C. It shows products that were sold but have no cost recorded.
D. It shows products that have a cost recorded irrespective of sales.
Answer: C
答案解析：
按照题意，查询出在sales表里的已经卖出去的但是不在costs表里的产品id。
INTERSECT operator, which returns only those unique rows returned by both queries返回共同有的唯一的行
MINUS Example The following statement combines results with the
MINUS operator, which returns only unique rows returned by the first query but not by the second
返回第一个有，第二个表无的行
官方参考：http://docs.oracle.com/cd/E11882_01/server.112/e41084/queries004.htm#i2054381