//oracle中extract()函数从oracle 9i中引入,用于从一个date或者interval类型中截取到特定的部分
//语法如下： EXTRACT ( { YEAR | MONTH | DAY | HOUR | MINUTE | SECOND }
| { TIMEZONE_HOUR | TIMEZONE_MINUTE }
| { TIMEZONE_REGION | TIMEZONE_ABBR }
FROM { date_value | interval_value } )
//我们只可以从一个date类型中截取 year,month,day(date日期的格式为yyyy-mm-dd);
//我们只可以从一个 timestamp with time zone 的数据类型中截取TIMEZONE_HOUR和TIMEZONE_MINUTE;
select extract(year from date'2011-05-17') year from dual;
YEAR ---------- 2011
select extract(month from date'2011-05-17') month from dual;
MONTH ---------- 5
select extract(day from date'2011-05-17') day from dual;
DAY ---------- 17
//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('2011-02-04 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)
/ DAY HOUR MINUTE SECOND ---------- ---------- ---------- ---------- 102 4 1 46
-- 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) ta
from dual
/ YEAR MONTH DAY MINUTE SECOND TH TM TR TA
---------- ---------- ---------- ---------- ---------- ---------- ---------- --------- ---------- 2011 5 17 7 14.843 8 0 UNKNOWN UNK
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