OCP认证051考试题库：11g-v9.02-第140题
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140. Examine the structure of the PRODUCTS table:
name Null Type
PROD_ID NOT NULL NUMBER(4)
PROD_NAME VARCHAR2(20)
PROD_STATUS VARCHAR2(6)
QTY_IN_HAND NUMBER(8,2)
UNIT_PRICE NUMBER(10,2)
You want to display the names of the products that have the highest total value for UNIT_PRICE *
QTY_IN_HAND.
Which SQL statement gives the required output?
A. SELECT prod_name
FROM products
WHERE (unit_price * qty_in_hand) = (SELECT MAX(unit_price * qty_in_hand)
FROM products);
B. SELECT prod_name
FROM products
WHERE (unit_price * qty_in_hand) = (SELECT MAX(unit_price * qty_in_hand)
FROM products
GROUP BY prod_name);
C. SELECT prod_name
FROM products
GROUP BY prod_name
HAVING MAX(unit_price * qty_in_hand) = (SELECT MAX(unit_price * qty_in_hand)
FROM products
GROUP BY prod_name);
D. SELECT prod_name
FROM products
WHERE (unit_price * qty_in_hand) = (SELECT MAX(SUM(unit_price * qty_in_hand))
FROM products)
GROUP BY prod_name;
Answer: A
试题解析：
BC都犯了一个错误，都会返回一个错误single-row subquery returns more than one row。
即是单行子查询返回了多行。该WHERE子句包含一个等于(=) 运算符，该运算符是一个只需要一个值的单行比较运算符。=运算符无法接受子查询中的多个值，因此产生了错误。
D的查询条件不满足题意。
