ORACLE中的单行函数 (2)

4、转换型函数

Round：四舍五入日期时间，可以是天，也可以是小时，分

EXP：

select round(sysdate,'MI') from dual;

select round(sysdate,'HH') from dual;

select round(sysdate) from dual;

Trunc：截断日期，可以是天，也可以是小时，分

Exp:

select trunc(sysdate,'MI') from dual;

cast:进行数据类型的转化

Exp：

select cast(sysdate as  varchar2(100)) from dual;

NUMTODSINTERVAL：将间隔指定为时分秒间隔类型

Exp：

SELECT SYSDATE

      ,SYSDATE+NUMTODSINTERVAL(2,'HOUR') "2 hours later"

      ,SYSDATE+NUMTODSINTERVAL(30,'MINUTE') "30 minutes later"

      ,sysdate+1/12

      ,sysdate+1/48

FROM dual;

NUMTOYMINTERVAL：转化间隔为年月类型

Exp：

SELECT SYSDATE

      ,SYSDATE+NUMTOYMINTERVAL(2,'YEAR') "2 years later"

      ,SYSDATE+NUMTOYMINTERVAL(6,'MONTH') "6 months later"

FROM dual;

To_char:转化日期和数字类型为字符类型

Exp：

SELECT TO_CHAR(SYSDATE, 'dd" day of "Month, YYYY" Quarter="q" weekday="day') from dual;

SELECT    to_char(sysdate,'" time="hh24-mi-ss.sssss" week of month="w" week of year="www') from dual;

select      to_char(sysdate, '"day of a week="d" day of year="ddd') from dual;

SELECT SYSDATE

      ,TO_CHAR(SYSDATE,'Mmspth') Month

      ,TO_CHAR(SYSDATE,'DDth') Day

      ,TO_CHAR(SYSDATE,'Yyyysp') Year

      ,TO_CHAR(SYSDATE,'year') Year

,TO_CHAR(SYSDATE,'YEAR') Year

FROM dual;

SELECT TO_CHAR(123456,'9.99999EEEE')

      ,TO_CHAR(123456,'9.9EEEE')

FROM dual;

To_number: 转化字符类型为数字类型

TO_DATE：字符类型转换为日期类型

Exp：

SQL> select      to_date('day of a week=3 day of year=115', '"day of a week="d" day of year="ddd') from dual;

TO_DATE('DAYOFAWEEK=3DAYOFYEAR

------------------------------

2012/4/24

TO_DSINTERVAL:转换为日期可以接受的INTERVAL DAY TO SECOND类型。

SELECT SYSDATE

      ,SYSDATE+TO_DSINTERVAL('007 12:00:00') "+7 1/2  days"

      ,SYSDATE+7.5 "+7 1/2  days"

FROM dual;