select sysdate from dual--return system time
select trunc(sysdate) from dual
select trunc(sysdate-8) from dual
select trunc(sysdate+8) from dual
select trunc(sysdate-to_date('2015-2-18','yyyy-MM-dd')) from dual--system time-specified time
select trunc(to_date('2015-2-20','yyyy-MM-dd')-8) from dual--specified time plus or minus days
select trunc(to_date('2015-2-20','yyyy-MM-dd')+8) from dual
select trunc(sysdate+(INTERVAL '1' DAY) ) from dual --加1天(1)
select trunc(sysdate+(INTERVAL '1' MONTH) ) from dual --加1月
select trunc(sysdate+(INTERVAL '1' YEAR) ) from dual --加1年
select trunc(to_date('2015-2-20','yyyy-MM-dd')+(INTERVAL '1' DAY)) from dual --加1天(1)
select sysdate,last_day(sysdate) from dual;--return the date of the last day of the month
select trunc(28.4), trunc(28.9), trunc(sysdate) from dual;--only integers
select round(28.4),round(28.9) from dual;--round 5 for all types 4
---
select to_date('2015-2-18','yyyy-MM-dd'),-- the date at that time,
round(to_date('2015-2-18','yyyy-MM-dd')),-- today's date,
round(to_date('2015-2-18','yyyy-MM-dd'),'day'),-- Sunday this week,
round(to_date('2015-2-18','yyyy-MM-dd'),'month') ,--the beginning of this month,
round(to_date('2015-2-18','yyyy-MM-dd'),'q'),-- the date of the beginning of the season,
round(to_date('2015-2-18','yyyy-MM-dd'),'year')-- the date at the beginning of the year
from dual;
--
select sysdate ,--the current date,
next_day(sysdate,'Monday'),-- Monday of the next week,
next_day(sysdate,'Tuesday'),-- Tuesday next week,
next_day(sysdate,'Wednesday'),-- Wednesday next week,
next_day(sysdate,'Thursday'),-- Thursday next week,
next_day(sysdate,'Friday'),-- Friday next week,
next_day(sysdate,'Saturday'),-- next Saturday,
next_day(sysdate,'Sunday')-- Sunday of the next week
from dual;
---
select
extract(hour from timestamp '2001-2-16 2:38:40 ' ),-- 小时,
extract(minute from timestamp '2001-2-16 2:38:40 ' ) ,--分钟,
extract(second from timestamp '2001-2-16 2:38:40 ' ),-- 秒,
extract(DAY from timestamp '2001-2-16 2:38:40 ' ) ,--日,
extract(MONTH from timestamp '2001-2-16 2:38:40 ' ) ,--月,
extract(YEAR from timestamp '2001-2-16 2:38:40 ' )-- 年
from dual;