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一、作用：从一个date（日期）类型或者interval（时间区间）类型中截取指定的部分。
二、范例：
获取系统当前时间
select sysdate from dual ;分别获取对应的年月日时分秒
(1)select (to_char(sysdate,‘YYYY‘)) from dual(2)select (to_char(sysdate,‘YEAR‘)) from dual(1)select (to_char(sysdate,‘MM‘)) from dual(2)select (to_char(sysdate,‘MONTH‘)) from dual(1)select (to_char(sysdate,‘DD‘)) from dual(2)select (to_char(sysdate,‘DAY‘)) from dualCREATE OR REPLACE FUNCTION xiaoxing_is_date(parameter VARCHAR2) RETURN NUMBER ISval DATE;BEGINval := TO_DATE(NVL(parameter, ‘a‘), ‘yyyy-mm-dd hh24:mi:ss‘);RETURN 1;EXCEPTIONWHEN OTHERS THENRETURN 0;END;select extract(year from sysdate) year from dual ;获取date中的月
select extract(month from sysdate) month from dual ;获取date中的天
select extract(day from sysdate) day from dual;获取两个日期之间具体的时间间隔
select to_timestamp(‘2015-02-15 22:22:22‘,‘yyyy-mm-dd hh24:mi:ss‘) from dual ;select to_date(‘2015-02-15 22:22:22‘,‘yyyy-mm-dd hh24:mi:ss‘) from dual ;select to_timestamp(‘2016-02-15 22:22:22‘, ‘yyyy-mm-dd hh24:mi:ss‘) -to_timestamp(‘2016-01-04 10:55:55‘, ‘yyyy-mm-dd hh24:mi:ss‘)from dual;select to_date(‘2016-02-15 22:22:22‘, ‘yyyy-mm-dd hh24:mi:ss‘) -to_date(‘2016-01-04 10:55:55‘, ‘yyyy-mm-dd hh24:mi:ss‘)from dual;select systimestamp from dual ;select extract(year from systimestamp) year,extract(month from systimestamp) month,extract(day from systimestamp) day,extract(minute from systimestamp) minute,extract(second from systimestamp) second,extract(timezone_hour from systimestamp) th,extract(timezone_minute from systimestamp) tm,extract(timezone_region from systimestamp) tr,extract(timezone_abbr from systimestamp) tafrom dual ;标签：
原文地址：http://www.cnblogs.com/yaoxiaoxing/p/5109892.html
