Choose the best answeride
Examine the description of the PRODUCT_INFORMATION table:函数
Name NULL? Typeorm
PROD_ID NOT NULL NUMBER(2)ip
PROD_NANE VARCRAR2 (10)产品
LIST_PRICE NUMBER(6,2)it
Which query retrieves the number of products with a null list price?io
A) SELECT (COUNT(list_price) FERM Product_intormation WHERE list_price=NULL;table
B) SELECT Count(nvl( list_price,0) )FROM pruduct_information WHERE list_price is null;form
C) SELECT COUNT(DISTINCT list_price) FROM produet_infomation WHERE list_price is nulll.class
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，题目的意思是哪一个查询可以检索到 price 为空的产品数量。因为 list_price 自己为空，count 函数处理的方式是忽略，因此要用 nvl 函数来处理。)