oracle 列别名使用注意

在sql查询中，合理的使用别名有很多好处
一：使用别名的好处
   1）简化SQL语句的书写，特别是多表关联查询且表名较长时
   2）增强SQL语句的可读性，特别是当查询出来的列字段较为复杂时效果更为明显
二.别名使用的注意事项
   1.可以使用as 也可以不使用
   2.不能使用单引号
   3.可以使用双引号或者不使用
   4.但是当别名中有特殊字符的时候，必须使用双引号
   5.当别名是关键字的时候，也需要用双引号，比如示例中的
   CUSTOMER-ID
　　DATE

附一ocp考题

Examine the description of the transactions table:

Examine the description of the transactions table:

Name                                         NULL?               TYPE

TRANSACTION_ID                NOT NULL          VARCHAR2(6)

TRANSACTION_DATE                                      DATE

AMOUNT                                                　　   NUMBER(10,2)

CUSTOMER_ID                                       　　 VARCHAR2(6)

Which two SQL statements execute successfully?

A.  SELECT customer_id AS "CUSTOMER-ID", transaction_date AS DATE, amount+100 "DUES" from transactions;

B.  SELECT customer_id AS 'CUSTOMER-ID',transaction_date AS DATE, amount+100 'DUES' from transactions;

C.  SELECT customer_id CUSTID, transaction_date TRANS_DATE，amount+100 DUES FROM transactions;

D.  SELECT customer_id AS "CUSTOMER-ID", transaction_date AS "DATE", amount+100 DUES FROM transactions;

E.  SELECT customer id AS CUSTOMER-ID, transaction_date AS TRANS_DATE, amount+100 "DUES AMOUNT"

FROM transactions;

Correct Answer:CD