OCP-1Z0-051-V9.02-64题

64. View the E xhibit and examine the data in the PROMO_CATEGORY and PROMO_COST columns of

the PROMOTIONS table.

Evaluate the following two queries:

SQL>SELECT DISTINCT promo_category   to_char(promo_cost)"code"    

FROM promotions    

ORDER BY code;

SQL>SELECT DISTINCT promo_category  promo_cost "code"    

FROM promotions    

ORDER BY 1;

Which statement is true regarding the execution of the above queries? 

A. Only the first query executes successfully.

B. Only the second query executes successfully.

C. Both queries execute successfully but give different results.

D. Both queries execute successfully and give the same result.

Answer: B

答案解析：

参考：http://blog.csdn.net/rlhua/article/details/12837221

order by 可以指定表达式、别名或列位置作为排序条件，别名要完全匹配

列别名并没有完全匹配，所以报错。

sh@TEST0924>  SELECT DISTINCT promo_category, to_char(promo_cost)"code"

  2  FROM promotions

  3  ORDER BY code;

ORDER BY code

         *

ERROR at line 3:

ORA-00904: "CODE": invalid identifier

 应该改为：

sh@TESTDB> SELECT DISTINCT promo_category, to_char(promo_cost)"code"

  2  FROM promotions

  3  where rownum<6

  4   ORDER BY "code";

 

PROMO_CATEGORY                 code

------------------------------ ----------------------------------------

NO PROMOTION                   0

newspaper                      200

post                           300

newspaper                      400

internet                       600

 第二个SQL如下，可执行成功，原题差一个逗号

sh@TESTDB> SELECT DISTINCT promo_category,promo_cost "code"

  2  FROM promotions

  3  where rownum<6

  4   ORDER BY 1;

 

PROMO_CATEGORY                       code

------------------------------ ----------

NO PROMOTION                            0

internet                              600

newspaper                             200

newspaper                             400

post                                  300