oracle中extract()函数----用于截取年、月、日、时、分、秒

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 } )

只可以从一个date类型中截取年月日

SQL> select extract (year from sysdate) year, extract (month from sysdate) month, extract (day from sysdate) day from dual;

  YEAR      MONTH        DAY

---

  2015          5          4

只可以从一个date类型中截取年月日

SQL> select extract (year from date ‘2015-05-04’) year, extract (month from date’2015-05-04’) month, extract (day from date ‘2011-05-04’) day from dual;

  YEAR      MONTH        DAY

---

  2015          5          4

从timestamp中获取年月日时分秒

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

获取两个日期之间的具体时间间隔
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
)

获取interval类型特定部分
select extract(year from interval ‘21’ year) year from dual
Interval 语法
interval ‘{ integer | integer time_expr | time_expr }’

{ { day | hour | minute } [ ( leading_precision ) ]

| second [ ( leading_precision [, fractional_seconds_precision ] ) ] }

[ to { day | hour | minute | second [ (fractional_seconds_precision) ] } ]

leading_precision值的范围是0到9, 默认是2. time_expr的格式为:hh[:mi[:ss[.n]]] or mi[:ss[.n]] or ss[.n], n表示微秒.

范围值:

hour: 0 to 23

minute: 0 to 59

second: 0 to 59.999999999

eg:

interval '4 5:12:10.222' day to second(3)                 表示: 4天5小时12分10.222秒

interval '4 5:12' day to minute                         表示: 4天5小时12分

interval '400 5' day(3) to hour                         表示: 400天5小时, 400为3为精度,所以"day(3)", 注意默认值为2.

interval '400' day(3)                                   表示: 400天

interval '11:12:10.2222222' hour to second(7)           表示: 11小时12分10.2222222秒

interval '11:20' hour to minute                         表示: 11小时20分

interval '10' hour                                      表示: 10小时

interval '10:22' minute to second                         表示: 10分22秒

interval '10' minute                                     表示: 10分

interval '4' day                                         表示: 4天

interval '25' hour                                         表示: 25小时

interval '40' minute                                     表示: 40分

interval '120' hour(3)                                     表示: 120小时

interval '30.12345' second(2,4)                         表示: 30.1235秒, 因为该地方秒的后面精度设置为4, 要进行四舍五入.

interval '20' day - interval '240' hour = interval '10-0' day to second 表示: 20天 - 240小时 = 10天0秒