156. Evaluate the following SQL statement:
SQL> SELECT cust_id, cust_last_name "Last Name"
FROM customers
WHERE country_id = 10
UNION
SELECT cust_id CUST_NO, cust_last_name
FROM customers
WHERE country_id = 30;
Which ORDER BY clauses are valid for the above query? (Choose all that apply.)
A. ORDER BY 2,1
B. ORDER BY CUST_NO
C. ORDER BY 2,cust_id
D. ORDER BY "CUST_NO"
E. ORDER BY "Last Name"
Answer: ACE
答案解析：
ORDER BY 后面可以跟数字，可以完全一摸一样的列名,经过union后，字段名根据第一个查询语句显示，变为cust_id和Last Name。
sh@TEST0924> SELECT cust_id, cust_last_name "Last Name" from customers where country_id=52770 and rownum<5
2 union
3 select cust_id CUST_NO,cust_last_name from customers where country_id=52775 and rownum<5;
CUST_ID Last Name
---------- ----------------------------------------
3228 Ruddy
6783 Ruddy
10338 Ruddy
13894 Ruddy
21005 Ruddy
37004 Embrey
40559 Embrey
49671 Ruddy
8 rows selected.
A答案：
sh@TEST0924> SELECT cust_id, cust_last_name "Last Name" from customers where country_id=52770 and rownum<5
2 union
3 select cust_id CUST_NO,cust_last_name from customers where country_id=52775 and rownum<5
4 ORDER BY 2,1;
CUST_ID Last Name
---------- ----------------------------------------
37004 Embrey
40559 Embrey
3228 Ruddy
6783 Ruddy
10338 Ruddy
13894 Ruddy
21005 Ruddy
49671 Ruddy
8 rows selected.
B答案：报错，没有CUST_NO字段。
sh@TEST0924> SELECT cust_id, cust_last_name "Last Name" from customers where country_id=52770 and rownum<5
2 union
3 select cust_id CUST_NO,cust_last_name from customers where country_id=52775 and rownum<5
4 ORDER BY CUST_NO;
ORDER BY CUST_NO
*
ERROR at line 4:
ORA-00904: "CUST_NO": invalid identifier
C答案：
sh@TEST0924> SELECT cust_id, cust_last_name "Last Name" from customers where country_id=52770 and rownum<5
2 union
3 select cust_id CUST_NO,cust_last_name from customers where country_id=52775 and rownum<5
4 ORDER BY 2,cust_id
5 ;
CUST_ID Last Name
---------- ----------------------------------------
37004 Embrey
40559 Embrey
3228 Ruddy
6783 Ruddy
10338 Ruddy
13894 Ruddy
21005 Ruddy
49671 Ruddy
8 rows selected.
D答案：报错
sh@TEST0924> SELECT cust_id, cust_last_name "Last Name" from customers where country_id=52770 and rownum<5
2 union
3 select cust_id CUST_NO,cust_last_name from customers where country_id=52775 and rownum<5
4 ORDER BY "CUST_NO"
5 ;
ORDER BY "CUST_NO"
*
ERROR at line 4:
ORA-00904: "CUST_NO": invalid identifier
E答案：
sh@TEST0924> SELECT cust_id, cust_last_name "Last Name" from customers where country_id=52770 and rownum<5
2 union
3 select cust_id CUST_NO,cust_last_name from customers where country_id=52775 and rownum<5
4 ORDER BY "Last Name"
5 ;
CUST_ID Last Name
---------- ----------------------------------------
37004 Embrey
40559 Embrey
3228 Ruddy
6783 Ruddy
10338 Ruddy
13894 Ruddy
21005 Ruddy
49671 Ruddy
8 rows selected.