概述
Q43. View the Exhibit and examine the description of the PRODUCT_INFORMATION table.
Which SQL statement would retrieve from the table the number of products having LIST_PRICE as NULL?
A. SELECT COUNT(list_price) FROM product_information WHERE list_price IS NULL;
B. SELECT COUNT(list_price) FROM product_information WHERE list_price = NULL;
C. SELECT COUNT(NVL(list_price, 0)) FROM product_information WHERE list_price IS NULL;
D. SELECT COUNT(DISTINCT list_price) FROM product_information WHERE list_price IS NULL;
Correct Answer: C
count(*) 含 重 复 的和 null
count(expr1) 含 重 复 不 含 null
count(distinct expr1) 不含重复不含 null
最后
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