日期型別變數的定義：to_date()函式

select  to_date('2018年11月9日 23時24分24秒','yyyy"年"mm"月"dd"日" hh24"時"mi"分"ss"秒"')
from dual;

------日期類單行函式
常規日期函式：
– 取日期值得某一部分
– 日期加減
– 日期舍入
時區類日期函式

1.取日期值得某一部分
– to_char函式

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

– extract()函式
會把date型別的變數處理成“年月日”.

SELECT extract(DAY FROM TO_DATE('2013-01-03 12:26:22','yyyy-mm-dd hh24-mi-ss')) FROM DUAL
 

timestamp型別變數可以提取HOUR,MINUTE,SECOND.

SELECT  extract(second from TO_timestamp('2013-01-03 12:26:22','yyyy-mm-dd hh24-mi-ss')) FROM DUAL

2.日期加法
直接加上數字

select date'2013-01-01'+29+1/12 from dual

add_months()函式

add_months(date'2012-02-29',24)=add_months(date'2012-02-28',24) 

interval()

select  date'2017-01-01'+interval'1-6' year(3) to month   from dual
select date'2013-04-17'+interval'1 23'day to hour from dual
 

NUMTOYMINTERVAL 和 NUMTODSINTERVAL

select date'2013-01-28'+numtoyminterval(1,'month') from dual
select date'2013-01-28'+numtodsinterval(31,'day') from dual

3.日期差值
直接相減

select date'2013-01-31'-to_date('2013-01-01 12:00:00','yyyy-mm-dd hh24:mi:ss') from dual

months_between函式

select months_between(date'2013-01-31',to_date('2010-11-01 12','yyyy-mm-dd hh24')) from dual;
 

4.日期舍入
– trunc函式

select trunc(to_date('12:35:35','hh24:mi:ss'),'MI') from dual;
select trunc(to_date('12:35:35','hh24:mi:ss'),'HH') from dual;

– ROUND函式

select round(date'2013-04-15','MM') from dual;
select round(to_date('12:35:35','hh24:mi:ss'),'MI') from dual;

5.其他常規函式
NEXT_DAY,LAST_DAY