oracle抽取函数-extract()

oracle抽取函数

 

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
------------------------------
                            10

以上是EXTRACT()函数的使用说明,extract 抽取年月日部分和时分部分的使用方法是不同的.
EXTRACT(YEAR FROM SYSDATE)中FROM 的下一个参数是日期类型的时候可以抽取年月日.就是说这个参数是日期类型的时候就
可以抽取年/月/日,而抽取不了时/分部分.抽取时分部分得在FROM 后面加带TIMESTAMP 且后面加时间字符

 

 这里要注意,在(MINUTE FROM TIMESTAMP '2010-10-10 10:10:10')中,如果把'2010-10-10 10:10:10'用日期类型的字段来代替
 并转换成字符类型后,也是错误的,估计是这方法的设计问题.

 

  比如(MINUTE FROM TIMESTAMP to_date(to_char(日期类型,'YYYY-MM-DD hh24:mi:ss'),'YYYY-MM-DD hh24:mi:ss')),这样执行不了的.

 

例如：
SQL> select extract(MINUTE FROM TIMESTAMP to_date(to_char(sysdate,'YYYY-MM-DD hh24:mi:ss'),'YYYY-MM-DD hh24:mi:ss')) from dual;

 

select extract(MINUTE FROM TIMESTAMP to_date(to_char(sysdate,'YYYY-MM-DD hh24:mi:ss'),'YYYY-MM-DD hh24:mi:ss')) from dual

ORA-00907: 缺失右括号

 

如果要从日期类型的字段中抽取时/分部分用to_char() 函数就可以.比如to_char(sysdate,'hh24')抽取小时

 

例如：

 

抽取小时

 

SQL> select to_char(sysdate,'hh24') from dual;

TO_CHAR(SYSDATE,'HH24')
---------------------------------------------------------------------------
21

 

抽取分钟

SQL> select to_char(sysdate,'mi') from dual;

TO_CHAR(SYSDATE,'MI')
---------------------------------------------------------------------------
48

 

抽取秒

SQL> select to_char(sysdate,'ss') from dual;

TO_CHAR(SYSDATE,'SS')
---------------------------------------------------------------------------
42

 

 

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