【2019年8月版】OCP 071认证考试原题-第37题

Choose the best answer

Examine the description of the PRODUCT_INFORMATION table:

Name NULL? Type

PROD_ID NOT NULL NUMBER(2)

PROD_NANE VARCRAR2 (10)

LIST_PRICE NUMBER(6,2)

Which query retrieves the number of products with a null list price?

A) SELECT (COUNT(list_price) FERM Product_intormation WHERE list_price=NULL;

B) SELECT Count(nvl( list_price,0) )FROM pruduct_information WHERE list_price is null;

C) SELECT COUNT(DISTINCT list_price) FROM produet_infomation WHERE list_price is nulll.

D) SELECT COUNT(list_price) from proceduct_information where list_price is NULL;

Answer：B

(解析：这道题的难点在题目的提问上，题目的意思是哪个查询能够检索到 price 为空的产品数量。由于 list_price 本身为空，count 函数处理的方式是忽略，所以要用 nvl 函数来处理。)