-EXTRACT

//Oracle中extract()函數從oracle 9i中引入,用于從一個date或者interval類型中截取到特定的部分

//語法如下：

EXTRACT (

{ YEAR | MONTH | DAY | HOUR | MINUTE | SECOND }

| { TIMEZONE_HOUR | TIMEZONE_MINUTE }

| { TIMEZONE_REGION | TIMEZONE_ABBR }

FROM { date_value | interval_value } )

//我們只可以從一個date類型中截取 year,month,day(date日期的格式為yyyy-mm-dd);

//我們只可以從一個 timestamp with time zone 的數據類型中截取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

//獲取兩個日期之間的具體時間間隔，extract函數是最好的選擇

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?? UN2K

-INTERVAL

以前對oracle時間類型數據的計算，都是直接加減。最近看到同事在使用INTERVAL，相對于之間幾分鐘要自己想想怎么通過計算式得來的方式，這種方式更直白。由于是使用字符類型，一下就可以看出來加減了多少時間。

INTERVAL

語法:

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值的范圍是0到9, 默認是2. time_expr的格式為:HH[:MI[:SS[.n]]] or MI[:SS[.n]] or SS[.n], n表示微秒.

INTERVAL '400 5' DAY(3) TO HOUR

表示: 400天5小時, 400為3為精度,所以"DAY(3)", 注意默認值為2

INTERVAL '30.12345' SECOND(2,4)

表示: 30.1235秒, 因為該地方秒的后面精度設置為4, 要進行四舍五入

select date '2010-01-01' + interval '21' year from dual

select date '2010-01-01' + interval '123-2' year(4) to month from dual

select date '2010-01-01' + interval '100' month from dual

select date '2010-01-01' + interval '100' day(2) from dual

select date '2010-01-01' + interval '1 2' day to hour from dual

select date '2010-01-01' + interval '1 2:3' day to minute from dual

select date '2010-01-01' + interval '1 2:3:4' day to second from dual

select date '2010-01-01' + interval '1' hour from dual

select date '2010-01-01' + interval '1:2' hour to minute from dual

select date '2010-01-01' + interval '1:2:3' hour to second from dual

select date '2010-01-01' + interval '1:2' minute to second from dual

interval之后也可以使用'-1'這樣的負，這樣就是相減了。

總結

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