147. View the Exhibit and examine the structure of the PROMOTIONS table.
Evaluate the following SQL statement:
SQL>SELECT promo_name,CASE
WHEN promo_cost >=(SELECT AVG(promo_cost)
FROM promotions
WHERE promo_category='TV')
then 'HIGH'
else 'LOW'
END COST_REMARK
FROM promotions;
Which statement is true regarding the outcome of the above query?
A. It shows COST_REMARK for all the promos in the table. 分类显示所有值
B. It produces an error because the subquery gives an error.
C. It shows COST_REMARK for all the promos in the promo category 'TV'.
D. It produces an error because subqueries cannot be used with the CASE expression.
Answer: A
答案解析：
1、首先运行子查询，得出一个数值
sh@TEST0910> SELECT AVG(promo_cost) FROM promotions WHERE promo_category='TV';
AVG(PROMO_COST)
---------------
46260.8696
2、所有的promos 根据上面计算的数值，来进行分类。故选择A
sh@TEST0910> SELECT promo_name,CASE WHEN promo_cost >=
2 (SELECT AVG(promo_cost) FROM promotions WHERE promo_category='TV')
3 then 'HIGH' else 'LOW'END COST_REMARK
4 FROM promotions;
PROMO_NAME COST
------------------------------ ----
NO PROMOTION # LOW
newspaper promotion #16-108 LOW
post promotion #20-232 LOW
newspaper promotion #16-349 LOW
internet promotion #14-471 LOW