一、原题
Which three statements are true regarding sub queries? (Choose three.)
A. Multiple columns or expressions can be compared between the main query and sub query
B. Main query and sub query can get data from different tables
C. Sub queries can contain GROUP BY and ORDER BY clauses
D. Main query and sub query must get data from the same tables
E. Sub queries can contain ORDER BY but not the GROUP BY clause
F. Only one column or expression can be compared between the main query and subqeury
答案: A,B,C
二、题目翻译
下列关于子查询的描述哪三项是正确的?（选择三项）
A.多列或表达式可以在主查询和子查询之间比较。
B.主查询和子查询可以从不同的表中获取数据。
C.子查询可以包含GROUP BY 和ORDER BY 子句。
D.主查询和子查询必须从相同的表中获取数据。
E.子查询可以包含ORDER BY子句，但是不能包含GROUP BY子句。
F.在主查询和子查询中，只能比较一列或表达式。
三、题目解析
主查询和子查询可以从不同的表中取数据，而且，子查询中可以包含GROUP BY 和ORDER BY 子句,也可以在主查询和子查询之间比较多列数据。