12、（5-12）choose two:
Examine the data in the CUSTOMERS table:
You want to list all cities that have more than one customer along with the customer details.
Evaluate the following query:
SQL>SELECT c1.custname, c1.city
FROM Customers c1__Customers c2
ON (c1.city=c2.city AND c1.custname<>c2.custname);

Which two JOIN options can be used in the blank in the above query to give the correct output?
A) NATURAL JOIN
B) RIGHT OUTER JOIN
C) LEFT OUTER JOIN
D) JOIN
E) FULL OUTER JOIN

Answer：BD
（解析：验证过
A 选项不正确，NATURAL JOIN 自然连接不需要关联条件，所以下面的 ON 子句会报错。
CE 选项不正确，LEFT OUTER JOIN 和 FULL OUTER JOIN 都会显示有客户但是没在某个城市的人
）