（156）Evaluate the following SQL statement:

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"

答案：（A、C、E）

解析：

ORDER BY子句中列的序号和列名可以混合使用

B（X），最后的结果集中不会有CUST_NO列，因为它与第一个查询的对应的列名不同，会使用第一个查询中的列名

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