OCP-1Z0-051-V9.02-125题

125. Examine the structure of the CUSTOMERS table:

name                Null           Type

CUSTNO              NOT NULL       NUMBER(3)

CUSTNAME            NOT NULL       VARCHAR2(25)

CUSTADDRESS                       VARCHAR2(35)

CUST_CREDIT_LIMIT                 NUMBER(5)

CUSTNO is the PRIMARY KEY in the table. You want to find out if any customers' details have been

entered more than once using different CUSTNO, by listing all the duplicate names.

Which two methods can you use to get the required result? (Choose two.)

A. self-join

B. subquery

C. full outer-join with self-join

D. left outer-join with self-join

E. right outer-join with self-join

Answer: AB

答案解析：

参考：http://blog.csdn.net/rlhua/article/details/12877591

题意：找到是否存在客户信息使用不同的CUSTNO录入了多次，显示所有重复的客户名称

自连接即是查询两次自身的表，首先根据客户信息来查看CUSTNO大于1的记录，然后再根据CUSTNO来显示客户名称。子查询也是一样。