select to_char(current_timestamp,'hh24') from dual;--当前时间戳

select current_timestamp from dual;

select sysdate from dual;--系统时间

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;

select to_char(sysdate,'Q') from dual; --获取季度

select to_char(sysdate,'iw') from dual;--周，按日历上的那种，每年有52或者53周

select to_char(sysdate,'hh') from dual;

select to_char(sysdate,'hh24') from dual;

select to_char(sysdate,'D') from dual;---周中的星期几

select to_char(sysdate,'ddd') from dual; ---一年中的第几天

select to_char(sysdate,'ww') from dual;--相当于iw，一年中的第几个星期

select to_char(sysdate,'w') from dual;--该月中的第几个星期

select to_date('2009-12-25 14:23:31','yyyy-mm-dd hh24:mi:ss') from dual;--记住格式

select to_char(sysdate,'yy/mm/dd hh24:mi:ss') from dual;

select to_char(sysdate,'mon') from dual;--11月或者nov

select to_char(sysdate,'month') from dual;--11月或者november

select to_char(sysdate,'dy') from dual;--当周第几天后fri

select to_char(sysdate,'day') from dual;--星期五或者friday

select to_char(sysdate,'mi'),to_char(sysdate-interval'7' minute,'mi') from dual;--当前时间减去7分钟

select to_char(sysdate,'hh24'),to_char(sysdate-interval'7' hour,'hh24') from dual;

select to_char(sysdate,'dd'),to_char(sysdate-interval'7' day,'dd') from dual;--

select sysdate,sysdate-interval'7' month from dual;

select sysdate,sysdate-interval'7' year from dual;

select sysdate,sysdate-8*interval '7' day from dual;

select to_char(last_day(to_date('2010-11-1','yyyy-mm-dd')),'dd') from dual;

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oracle数据库中时间和日期的处理