YYYY/MM/DD HH:MI:SS -- 年/月/日 時(非24小時制):分:秒
J -- Julian day，Bc 4712/01/01 為1
RR/MM/DD -- 公元2000問題
-- 00-49 = 下世紀；50-99 = 本世紀
ex.
select to_char(sysdate,'YYYY/MM/DD') FROM DUAL; -- 2007/09/20
select to_char(sysdate,'YYYY') FROM DUAL; -- 2007
select to_char(sysdate,'YYY') FROM DUAL; -- 007
select to_char(sysdate,'YY') FROM DUAL; -- 07
select to_char(sysdate,'MM') FROM DUAL; -- 09
select to_char(sysdate,'DD') FROM DUAL; -- 20
select to_char(sysdate,'D') FROM DUAL; -- 5
select to_char(sysdate,'DDD') FROM DUAL; -- 263
select to_char(sysdate,'WW') FROM DUAL; -- 38
select to_char(sysdate,'W') FROM DUAL; -- 3
select to_char(sysdate,'YYYY/MM/DD HH24:MI:SS') FROM DUAL; -- 2007/09/20 15:24:13
select to_char(sysdate,'YYYY/MM/DD HH:MI:SS') FROM DUAL; -- 2007/09/20 03:25:23
select to_char(sysdate,'J') FROM DUAL; -- 2454364
select to_char(sysdate,'RR/MM/DD') FROM DUAL; -- 07/09/20
二.ROUND函数
SELECT ROUND( number, [ decimal_places ] ) FROM DUAL
说明：
number : 将要处理的数值
decimal_places : 四舍五入，小数取几位,不填默认为0
Sample :
select round(123.456) from dual; 结果： 123
select round(123.456, 0) from dual; 结果： 123
select round(123.456, 1) from dual; 结果： 123.5
select round(123.456, 2) from dual; 结果：123.46
select round(123.456, 3) from dual; 结果： 123.456
select round(-123.456, 2) from dual; 结果：-123.46