18. Examine the structure of the PROMOTIONS table:
name Null Type
PROMO_ID NOT NULL NUMBER(6)
PROMO_NAME NOT NULL VARCHAR2(30)
PROMO_CATEGORY NOT NULL VARCHAR2(30)
PROMO_COST NOT NULL NUMBER(10,2)
The management wants to see a report of unique promotion costs in each promotion category.
Which query would achieve the required result?
( 题意:题目给出了一个PROMOTIONS表的结构,需要打印出每个促销品种中不同的促销价格的报表,问,下面哪条查询语句能够满足这个要求?) A. SELECT DISTINCT promo_cost, promo_category FROM promotions; B. SELECT promo_category, DISTINCT promo_cost FROM promotions; C. SELECT DISTINCT promo_cost, DISTINCT promo_category FROM promotions; D. SELECT DISTINCT promo_category, promo_cost FROM promotions ORDER BY 1;