oracle抽取函数 extract()

auhtor：skate
time：2010/03/03
oracle抽取函数
今天朋友问个问题，如何抽取时间的“小时”
oracle的抽取函数是 extrac()语法:
SELECT EXTRACT(YEAR from SYSDATE) from DUAL; return Current Year
SELECT EXTRACT(MONTH from SYSDATE) from DUAL; return Current Month
SELECT EXTRACT(DAY from SYSDATE) from DUAL; return Current Day
SELECT EXTRACT(HOUR from TIMESTAMP '2010-10-10 10:10:10') from DUAL;
SELECT EXTRACT(MINUTE  from TIMESTAMP '2010-10-10 10:10:10') from DUAL;
例子如下：
SQL> SELECT EXTRACT(YEAR from SYSDATE) from DUAL
  2  ;
EXTRACT(YEARfromSYSDATE)
------------------------
                    2010
SQL> SELECT EXTRACT(month from SYSDATE) from DUAL
  2  ;
EXTRACT(MONTHfromSYSDATE)
-------------------------
                        3
SQL> SELECT EXTRACT(day from SYSDATE) from DUAL;
EXTRACT(DAYfromSYSDATE)
-----------------------
                      3
SQL> SELECT EXTRACT(hour from SYSDATE) from DUAL;
SELECT EXTRACT(hour from SYSDATE) from DUAL
ORA-30076: 对析出来源无效的析出字段
SQL> SELECT EXTRACT(minute from SYSDATE) from DUAL;
SELECT EXTRACT(minute from SYSDATE) from DUAL
ORA-30076: 对析出来源无效的析出字段
SQL> SELECT EXTRACT(HOUR from TIMESTAMP '2010-10-10 10:10:10') from DUAL;
EXTRACT(HOURfromTIMESTAMP'2010
------------------------------
                            10
SQL> SELECT EXTRACT(minute from TIMESTAMP '2010-10-10 10:10:10') from DUAL;
EXTRACT(MINUTEfromTIMESTAMP'20
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