//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
//