oracle增强型时间类型以及postgresql时间类型
oracle
date 包含时间和日期类型，包括年月日，小时，分钟，秒。这个经常用，相信大家都熟悉
timestamp 这个类型很精确，是精确到微妙的时间单位。指定精度的小数位，最多为9位，默认6位
timestamp with time zone 这个除了包含了timestamp的外，又有了时区。
timstamp with local time zone 这个类型不包含时区偏移量，由用户当地会话时区确定。
interval year to month
interval day to second
timestamp可以通过to_timestamp_t转换到timestamp with time zone
tz_offset可以查看时区的差位移
查看数据库时区：
SELECT dbtimezone FROM dual;
select sessiontimezone from dual;
SQL> select extract(year from sysdate) from dual;--获取年份
EXTRACT(YEARFROMSYSDATE)
------------------------
2012
SQL> select extract(month from sysdate) from dual;--获取月份
EXTRACT(MONTHFROMSYSDATE)
-------------------------
9
SQL> select extract(day from sysdate) from dual;--获取日
EXTRACT(DAYFROMSYSDATE)
-----------------------
6
SQL> select from_tz(timestamp '2012-09-06 09:00:00','8:00') from dual; --timestamp转timestamp with time zone
FROM_TZ(TIMESTAMP'2012-09-0609:00:00','8:00')
---------------------------------------------------------------------------
06-SEP-12 09.00.00.000000000 AM +08:00
SQL> create table test_zone
2 (timestamp_dt TIMESTAMP,
3 zone_dt TIMESTAMP WITH TIME ZONE,
4 local_zone_dt TIMESTAMP WITH LOCAL TIME ZONE);
Table created.
SQL> insert into test_zone values (sysdate,sysdate,sysdate);
1 row created.
SQL> col TIMESTAMP_DT for a35
SQL> col ZONE_DT for a35
SQL> col LOCAL_ZONE_DT for a35
SQL> select * from test_zone;
TIMESTAMP_DT ZONE_DT LOCAL_ZONE_DT
----------------------------------- ----------------------------------- -----------------------------------
06-SEP-12 01.50.10.000000 PM 06-SEP-12 01.50.10.000000 PM +08:00 06-SEP-12 01.50.10.000000 PM
SQL> insert into test_zone values(to_date('20090101','yyyymmdd'),to_timestamp('20090101','yyyymmdd'),to_timestamp_tz('20090101 010101 -8:00','yyyymmdd hh24miss TZH:TZM'));
1 row created.
SQL> select * from test_zone;
TIMESTAMP_DT ZONE_DT LOCAL_ZONE_DT
----------------------------------- ----------------------------------- -----------------------------------
06-SEP-12 01.50.10.000000 PM 06-SEP-12 01.50.10.000000 PM +08:00 06-SEP-12 01.50.10.000000 PM
01-JAN-09 12.00.00.000000 AM 01-JAN-09 12.00.00.000000 AM +08:00 01-JAN-09 05.01.01.000000 PM
SQL> alter session set time_zone='+05:00';
Session altered.
SQL> select * from test_zone;
TIMESTAMP_DT ZONE_DT LOCAL_ZONE_DT (提前了三个小时)
----------------------------------- ----------------------------------- -----------------------------------
06-SEP-12 01.50.10.000000 PM 06-SEP-12 01.50.10.000000 PM +08:00 06-SEP-12 10.50.10.000000 AM
01-JAN-09 12.00.00.000000 AM 01-JAN-09 12.00.00.000000 AM +08:00 01-JAN-09 02.01.01.000000 PM
SQL> select * from v$timezone_names where rownum<10; --查看时区名称
TZNAME TZABBREV
---------------------------------------------------------------- ----------------------------------------------------------------
Africa/Abidjan LMT
Africa/Abidjan GMT
Africa/Accra LMT
Africa/Accra GMT
Africa/Accra GHST
Africa/Addis_Ababa LMT
Africa/Addis_Ababa ADMT
Africa/Addis_Ababa EAT
Africa/Algiers LMT
SQL> select tz_offset('Africa/Accra') from dual;
TZ_OFFS
-------
+00:00
alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';--设置会话日期显示格式
SQL> select to_timestamp('20120909 00:01:02.123456789','yyyymmdd hh24:mi:ss.ff') from dual; --to_timestamp函数使用
TO_TIMESTAMP('2012090900:01:02.123456789','YYYYMMDDHH24:MI:SS.FF')
---------------------------------------------------------------------------
09-SEP-12 12.01.02.123456789 AM
SQL> select to_timestamp_tz('20120909 00:01:02.123456789 0:0','yyyymmdd hh24:mi:ss.ff tzh:tzm') from dual; --to_timestamp_tz
