OCP-1Z0-051-V9.02-151题

151. View the Exhibit and examine the structure of the CUSTOMERS and CUST_HISTORY tables.

The CUSTOMERS  table  contains  the  current  location  of  all  currently  active  customers. The

CUST_HISTORY table stores historical details relating to any changes in the location of all current as well

as previous customers who are no longer active with the company.

You need to find those customers who have never changed their address.

Which SET operator would you use to get the required output? 

A. MINUS

B. UNION

C. INTERSECT

D. UNION ALL

Answer: A

 

答案解析：

本题意是让找出没有改变过地址的客户。即从CUSTOMERS  减去改变过地址的CUST_HISTORY 的客户即可。

 

UNION Example The following statement combines the results of two queries with the UNION operator, which eliminates duplicate selected rows. This statement shows that you must match data type (using the TO_CHAR function) when columns do not exist in one or the other table

所有的行都包括

UNION ALL Example The UNION operator returns only distinct rows that appear in either result, while the UNION ALL operator returns all rows. The UNION ALL operator does not eliminate duplicate selected rows

去除重复的行

INTERSECT Example The following statement combines the results with the INTERSECT operator, which returns only those unique rows returned by both queries

返回共同有的唯一的行

MINUS Example The following statement combines results with the MINUS operator, which returns only unique rows returned by the first query but not by the second

返回第一个有，第二个表无的行

官方参考：http://docs.oracle.com/cd/E11882_01/server.112/e41084/queries004.htm#i2054381