【2019年8月版】OCP071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。)
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