一、原题
Which two statements are true regarding the USING clause in table joins? (Choose two.)
A.It can be used to join a maximum of three tables.
B.It can be used to restrict the number of columns used in a NATURAL join.
C.It can be used to access data from tables through equijoins as well as nonequijoins.
D.It can be used to join tables that have columns with the same name and compatible data types.
答案: BD
二、题目翻译
关于表连接中的USING子句的使用，下面的哪两个描述是正确的？(选择两项)
A.最多可以连接三张表。
B.可以用来限制NATURAL join(自然连接)中的列的数量。
C.可以用在等值连接和非等值连接。
D.可以用来连接有相同名字和一致的数据类型的列。
自然连接的详细用法，详见：
http://blog.csdn.net/holly2008/article/details/25501343