Oracle数据库中如何对时间格式进行处理

SQL>select to_char(sysdate,'YYYY-MM-DD HH12:MI:SS AM')from dual;

TO_CHAR(SYSDATE,'YYYY-MM-DDHH1
------------------------------
2007-06-29 02:50:06 下午

SQL>  select to_char(sysdate,'YYYY-MM-DD HH24:MI:SS AM')from dual;

TO_CHAR(SYSDATE,'YYYY-MM-DDHH2
------------------------------
2007-06-29 15:00:58 下午

select to_char(Sysdate-1/21/60,'HH24:MI:SS')from dual;

TO_CHAR(SYSDATE-1/21/60,'HH24:
------------------------------
15:00:54

select to_char(Sysdate+1/21/60,'HH24:MI:SS')from dual;

TO_CHAR(SYSDATE+1/21/60,'HH24:
------------------------------
15:03:53

select to_char(Sysdate-1/24,'HH24:MI:SS')from dual;

TO_CHAR(SYSDATE-1/24,'HH24:MI:
------------------------------
14:03:13

select to_char(Sysdate+1/24,'HH24:MI:SS')from dual;

TO_CHAR(SYSDATE+1/24,'HH24:MI:
------------------------------
16:03:32

select to_char(Sysdate+1,'YYYY-MM-DD')from dual;

TO_CHAR(SYSDATE+1,'YYYY-MM-DD'
------------------------------
2007-06-30