99.View the Exhibit and examine the structure of the PROMOTIONS table.

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于 2016-03-04 16:09:39 发布

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本文通过一个具体的SQL案例，展示了如何使用CASE语句结合AVG函数来计算不同条件下的平均成本。此方法适用于对特定区间的数据进行分组统计。

99.View the Exhibit and examine the structure of the PROMOTIONS table.

Using the PROMOTIONS table, you need to find out the average cost for all promos in the ranges
$0-2000 and $2000-5000 in category A
You issue the following SQL statement:

SQL>SELECT AVG(CASE WHEN promo_cost BETWEEN 0 AND 2000 AND promo_category='A'
then promo_cost ELSE null END) "CAT_2000A",
AVG(CASE WHEN promo_cost BETWEEN 2001 AND 5000 AND promo_category='A'
THEN promo_cost ELSE null END) "CAT_5000A"
FROM promotions;
What would be the outcome?
A.It executes successfully and gives the required result.
B.It generates an error because NULL cannot be specified as a return value.
C.It generates an error because CASE cannot be used with group functions.
D.It generates an error because multiple conditions cannot be specified for the WHEN clause.
答案：A
解析：这里case是用法