select sysdate from dual; select to_char(sysdate,'YYYY-MM-DD HH24:MI:SS') FROM DUAL; select systimestamp from dual; select add_months(sysdate,-2) from dual; --add_months (date,integer) -- date: 日期 ，integer 要加的月数 ，如果是负数，表示减去的月份数 select last_day(to_date('2017-2-1','yyyy-mm-dd')) from dual; --last_day 返回指定月份的最后一天 select next_day(sysdate,'星期二') from dual; --next_day(date,char)返回当前日期后一周对应的char的日期 ，char 表示是日期 select EXTRACT(YEAR FROM DATE '1998-03-07') from dual; --EXTRACT(datetime) 日期中提取年，月，日，分等 select extract(month from sysdate) from dual; select extract(day from date '2017-05-12') as day,extract(hour from timestamp '2017-05-12 15:14:16') as hours,extract(minute from timestamp '2017-05-12 15:14:16') as min,extract(second from timestamp '2017-05-12 15:14:16') as sec from dual; --获取两个日期之间的具体时间间隔，extract函数是最好的选择 select extract(day from dt2-dt1) day,extract(hour from dt2-dt1) hour,extract(minute from dt2-dt1) minute,extract(second from dt2-dt1) second from ( select to_timestamp('2011-05-04 15:07:00','yyyy-mm-dd hh24:mi:ss') dt1,to_timestamp('2011-05-17 19:08:46','yyyy-mm-dd hh24:mi:ss') dt2 from dual) / --months_between months_between(date1,date2) 返回date1到date2的月份数 select months_between(to_date('2010-12-01','YYYY-MM-DD'),to_date('2010-09-01','YYYY-MM-DD')) from dual;