[每日一题] OCP1z0-047 :2013-07-18时间格式

这道题目是考时间格式，日期的存贮格式，在ORACLE内部都由如下七部分构成：世纪、年、月、日、小时、分钟、秒。

OK,我们来做个测试：

gyj@OCM> create table gyj_order(order_id int,order_date date);
Table created.
gyj@OCM> insert into gyj_order values(1,sysdate);

1 row created.
gyj@OCM> commit;
Commit complete.
gyj@OCM> select * from gyj_order where order_date> to_date('JUL 10  2006','MON DDYYYY');

  ORDER_IDORDER_DAT
---------- ---------
         116-JUL-13
说明答案A正确

gyj@OCM> select * from gyj_order whereto_char(order_date,'MON DD YYYY')='JUL 16 2013';

  ORDER_IDORDER_DAT
---------- ---------
         116-JUL-13
说明答案B正确

gyj@OCM> select to_char(add_months(sysdate,6),'MONDD YYYY') from dual;

TO_CHAR(ADD_MO
--------------
JAN 16 2014
gyj@OCM> select * from gyj_order whereorder_date> to_char(add_months(sysdate,6),'MON DD YYYY');
select * from gyj_order where order_date>to_char(add_months(sysdate,6),'MON DD YYYY')
                                          *
ERROR at line 1:
ORA-01858: a non-numeric character was found where anumeric was expected

说明答案C不正确，时间类型与字符类型不能做比较

gyj@OCM> select * from gyj_order where order_datein(to_date('JUL 16 2013','MON DD YYYY'),to_char('JUL 16 2013','MON DD YYYY'));
select * from gyj_order where order_datein(to_date('JUL 16 2013','MON DD YYYY'),to_char('JUL 16 2013','MON DD YYYY'))
                                                                                        *
ERROR at line 1:
ORA-01722: invalid number


gyj@OCM> select to_char('JUL 16 2013','MON DDYYYY') from dual; select to_char('JUL 16 2013','MON DD YYYY') from dual
              *
ERROR at line 1:
ORA-01722: invalid number

上面的写法是错的，已是字符就无须用to_char转化，看下面的写法才是正确的：

gyj@OCM> select to_char(to_date('JUL 16 2013','MONDD YYYY'),'MON DD YYYY') from dual;

TO_CHAR(TO_
-----------
JUL 16 2013

还有时间与字符类型不能直接计算，如下报错：

gyj@OCM> select * from gyj_order where order_datein(to_char(to_date('JUL 16 2013','MON DD YYYY'),'MON DD YYYY'));
select * from gyj_order where order_datein(to_char(to_date('JUL 16 2013','MON DD YYYY'),'MON DD YYYY'))
                                            *
ERROR at line 1:
ORA-01858: a non-numeric character was found where anumeric was expected

答案D不正确

最终正确答案选：AB