OCP-1Z0-051-V9.02-110题

110. View the Exhibit and examine the structure of the CUSTOMERS table.

Using the CUSTOMERS table, you need to generate a report that shows   the average credit limit for

customers in WASHINGTON and NEW YORK.

Which SQL statement would produce   the required result? 

A. SELECT cust_city, AVG(cust_credit_limit)

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK')

GROUP BY cust_credit_limit, cust_city;

B. SELECT cust_city, AVG(cust_credit_limit)

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK')

GROUP BY cust_city,cust_credit_limit;

C. SELECT cust_city, AVG(cust_credit_limit)

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK')

GROUP BY cust_city; 按照城市来取平均值

D. SELECT cust_city, AVG(NVL(cust_credit_limit,0))

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK');

Answer: C

答案解析：

A答案：此处是按照cust_credit_limit, cust_city;这两个一起分组的。此处换另外两个城市来测试。

sh@TEST0924> SELECT cust_city,AVG(cust_credit_limit) FROM customers WHERE cust_city IN ('Duncan','Norman')

  2  GROUP BY cust_credit_limit, cust_city;

 

CUST_CITY                      AVG(CUST_CREDIT_LIMIT)

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

Norman                                           1500

Duncan                                           9000

Duncan                                          11000

Norman                                           3000

Norman                                           5000

Duncan                                           3000

Norman                                          11000

Duncan                                           5000

Norman                                          10000

Duncan                                           1500

Duncan                                           7000

Norman                                           9000

Duncan                                          10000

Duncan                                          15000

Norman                                           7000

Norman                                          15000

 

16 rows selected.

 

B答案，与A答案一样，按照cust_credit_limit, cust_city;这两个一起分组的。

 

C答案，按照cust_city来分组，与题意复合

h@TEST0924> SELECT cust_city,AVG(cust_credit_limit) FROM customers WHERE cust_city IN ('Duncan','Norman')

  2  GROUP BY cust_city;

 

CUST_CITY                      AVG(CUST_CREDIT_LIMIT)

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

Duncan                                           6550

Norman                                     6634.92063

 

D答案：缺少group by

sh@TEST0924> SELECT cust_city, AVG(NVL(cust_credit_limit,0)) FROM customers WHERE cust_city IN ('Duncan','Norman');

SELECT cust_city, AVG(NVL(cust_credit_limit,0)) FROM customers WHERE cust_city IN ('Duncan','Norman')

       *

ERROR at line 1:

ORA-00937: not a single-group group function

 

 

sh@TEST0924> SELECT cust_city, AVG(NVL(cust_credit_limit,0)) FROM customers WHERE cust_city IN ('Duncan','Norman')

  2  GROUP BY cust_city;

 

CUST_CITY                      AVG(NVL(CUST_CREDIT_LIMIT,0))

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

Duncan                                                  6550

Norman                                            6634.92063