121.Which two statements are true regarding the USING clause in table joins? (Choose two .)

121.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

解析：using，只能用于inner连接,using里面的字段不能加别名,包括where和select 语句中的，natural join 是只要连接的表的名字相同

就认为相等，而using是只有它指定的才相等，指定的列类型可以不同，但是可以隐式转换