18.Examine the structure of the PROMOTIONS table:

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?

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;

答案：D

解析：考察distinct，参考14题，BC不正确，题目说是要求唯一的promotion costs，其实AD都可以的，

如果非要选择一个的话，D是显示目录，后面是价格。显示比较友好，A和D就是显示和排序不一样