OCP-1Z0-051-V9.02-18题

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;

sh@TESTDB> SELECT DISTINCT promo_cost, promo_category FROM promotions where rownum<6;

PROMO_COST PROMO_CATEGORY
---------- ------------------------------
         0 NO PROMOTION
       200 newspaper
       300 post
       600 internet
       400 newspaper

 

B. SELECT promo_category, DISTINCT promo_cost FROM promotions;

sh@TESTDB> SELECT promo_category, DISTINCT promo_cost FROM promotions
  2  ;
SELECT promo_category, DISTINCT promo_cost FROM promotions
                       *
ERROR at line 1:
ORA-00936: missing expression

 

C. SELECT DISTINCT promo_cost, DISTINCT promo_category FROM promotions;

sh@TESTDB> SELECT DISTINCT promo_cost, DISTINCT promo_category FROM promotions;
SELECT DISTINCT promo_cost, DISTINCT promo_category FROM promotions
                            *
ERROR at line 1:
ORA-00936: missing expression

 

D. SELECT DISTINCT promo_category, promo_cost FROM promotions ORDER BY 1;

sh@TESTDB> SELECT DISTINCT promo_category, promo_cost FROM promotions where rownum<6 order by 1;

PROMO_CATEGORY                 PROMO_COST
------------------------------ ----------
NO PROMOTION                            0
internet                              600
newspaper                             200
newspaper                             400
post                                  300

 

unique promotion costs in each promotion category

promotion category前加DISTINCT

A与描述的不一致

BC语法错误，DISTINCT放在第二列要报错。

此题答案选D