OCP 1Z0 051 156

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" 

上节刚做过试验。在这个语句中只能
order by 1
order by 2
order by cust_id
order by "Last Name" 
其它统统都是错的
其实这样理解还容易些

SELECT *  FROM (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);

再在看后面order by 能跟什么？

Answer: ACE