Oracle中的时间函数用法to_date和to_char

一、24小时的形式显示出来要用HH24

select to_char(sysdate,'yyyy-MM-dd HH24:mi:ss') from dual;

select to_date('2005-01-01 13:14:20','yyyy-MM-dd HH24:mi:ss') from dual;

二、to_date() function

1.日期格式参数含义说明 

D一周中的星期几 

DAY天的名字，使用空格填充到9个字符 

DD月中的第几天 

DDD年中的第几天 

DY天的简写名 

IW ISO标准的年中的第几周 

IYYY ISO标准的四位年份 

YYYY四位年份 

YYY,YY,Y年份的最后三位，两位，一位 

HH小时，按12小时计 

HH24小时，按24小时计 

MI分 

SS秒 

MM月 

Mon月份的简写 

Month月份的全名 

W该月的第几个星期 

WW年中的第几个星期     1.日期时间间隔操作

当前时间减去7分钟的时间

select sysdate,sysdate - interval '7' MINUTE from dual

当前时间减去7小时的时间

select sysdate - interval '7' hour from dual

当前时间减去7天的时间

select sysdate - interval '7' day from dual

当前时间减去7月的时间

select sysdate,sysdate - interval '7' month from dual

当前时间减去7年的时间

select sysdate,sysdate - interval '7' year from dual

时间间隔乘以一个数字

select sysdate,sysdate - 8 *interval '2' hour from dual

2.1.日期到字符操作

select sysdate,to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual

select sysdate,to_char(sysdate,'yyyy-mm-dd hh:mi:ss') from dual

select sysdate,to_char(sysdate,'yyyy-ddd hh:mi:ss') from dual

select sysdate,to_char(sysdate,'yyyy-mm iw-d hh:mi:ss') from dual

2.2.字符到日期操作

select to_date('2003-10-17 21:15:37','yyyy-mm-dd hh24:mi:ss') from dual

2.3.oracle有毫秒级的数据类型

--返回当前时间年月日小时分秒毫秒

select to_char(current_timestamp(5),'DD-MON-YYYY HH24:MI:SSxFF') from dual;

--返回当前时间的秒毫秒，可以指定秒后面的精度(最大=9)

select to_char(current_timestamp(9),'MI:SSxFF') from dual;

2.4.计算程序运行的时间(ms)

declare

type rc is ref cursor;

l_rc rc;

l_dummy all_objects.object_name%type;

l_start number default dbms_utility.get_time;

begin

for I in 1 .. 1000

loop

open l_rc for

'select object_name from all_objects '||

'where object_id = ' || i;

fetch l_rc into l_dummy;

close l_rc;

end loop;

dbms_output.put_line

( round( (dbms_utility.get_time-l_start)/100, 2 ) ||

' seconds...' );

end;

三、to_char() function

The following are number examples for theto_charfunction.

 

to_char(1210.73, '9999.9')	would return '1210.7'
to_char(1210.73, '9,999.99')	would return '1,210.73'
to_char(1210.73, '$9,999.00')	would return '$1,210.73'
to_char(21, '000099')	would return '000021'

The following is a list of valid parameters when theto_charfunction is used to convert a date to a string. These parameters can be used in many combinations.

 

Parameter	Explanation
YEAR	Year, spelled out
YYYY	4-digit year
YYY YY Y	Last 3, 2, or 1 digit(s) of year.
IYY IY I	Last 3, 2, or 1 digit(s) of ISO year.
IYYY	4-digit year ｂａｓｅd on the ISO standard
Q	Quarter of year (1, 2, 3, 4; JAN-MAR = 1).
MM	Month (01-12; JAN = 01).
MON	Abbreviated name of month.
MONTH	Name of month, padded with blanks to length of 9 characters.
RM	Roman numeral month (I-XII; JAN = I).
WW	Week of year (1-53) where week 1 starts on the first day of the year and continues to the seventh day of the year.
W	Week of month (1-5) where week 1 starts on the first day of the month and ends on the seventh.
IW	Week of year (1-52 or 1-53) ｂａｓｅd on the ISO standard.
D	Day of week (1-7).
DAY	Name of day.
DD	Day of month (1-31).
DDD	Day of year (1-366).
DY	Abbreviated name of day.
J	Julian day; the number of days since January 1, 4712 BC.
HH	Hour of day (1-12).
HH12	Hour of day (1-12).
HH24	Hour of day (0-23).
MI	Minute (0-59).
SS	Second (0-59).
SSSSS	Seconds past midnight (0-86399).
FF	Fractional seconds.

The following are date examples for theto_charfunction.

 

to_char(sysdate, 'yyyy/mm/dd');	would return '2003/07/09'
to_char(sysdate, 'Month DD, YYYY');	would return 'July 09, 2003'
to_char(sysdate, 'FMMonth DD, YYYY');	would return 'July 9, 2003'
to_char(sysdate, 'MON DDth, YYYY');	would return 'JUL 09TH, 2003'
to_char(sysdate, 'FMMON DDth, YYYY');	would return 'JUL 9TH, 2003'
to_char(sysdate, 'FMMon ddth, YYYY');	would return 'Jul 9th, 2003'

You will notice that in some examples, theformat_maskparameter begins with "FM". This means that zeros and blanks are suppressed. This can be seen in the examples below.

 

to_char(sysdate, 'FMMonth DD, YYYY');	would return 'July 9, 2003'
to_char(sysdate, 'FMMON DDth, YYYY');	would return 'JUL 9TH, 2003'
to_char(sysdate, 'FMMon ddth, YYYY');	would return 'Jul 9th, 2003'

The zeros have been suppressed so that the day component shows as "9" as opposed to "09".

四、Oracle函数to_char转化数字型指定小数点位数的用法

to_char，函数功能，就是将数值型或者日期型转化为字符型。

比如最简单的应用：

/*1.0123--->'1.0123'*/
Select TO_CHAR(1.0123) FROM DUAL
/*123--->'123'*/
Select TO_CHAR(123) FROM DUAL

 接下来再看看下面：

/*0.123 ---> '.123' */
SELEC TO_CHAR(0.123) FROM DUAL

 上面的结果'.123'在大多数情况下都不是我们想要的结果，我们想要的应该是'0.123'。

我们来看一下to_char函数的具体用法：

TO_CHAR ( n [, fmt [, 'nlsparam']] )

该函数将NUMBER类型的n按数值格式fmt转换成VARCHAR2类型的值。'nlsparams'指定由数值格式的元素返回的字符,包括:

．小数点字符

．组分隔符

．本地钱币符号

．国际钱币符号

变元的形式为：

'NLS_NUMERIC_CHARACTERS="dg" NLS_CURRENCY="tcxt" NLS_ISO_CURRENCY=territory'

其中d为小数点字符,g为组分隔符。

例 :TO_CHAR (17145,'L099G999','NLS_NUMERIC_CHARACTERS=".," NLS_CURRENCY="NUD"')=NUD017,145

通过上面的了解，再查看fmt的一些格式，我们可以用以下表达式得到'0.123'的值：

/*0.123 ---> ' 0.123' */ 
Select TO_CHAR(0.123,'0.999') FROM DUAL
/*100.12 ---> '######' */ 
Select TO_CHAR(100.12,'0.999') FROM DUAL
/*1.12 ---> ' 1.120' */ 
Select TO_CHAR(1.12,'0.999') FROM DUAL

 ' 0.123'是出来了，可是前面又多了一个空格。

对于100.12的值却是######，以及'1.12'的值变成了'1.120'。

我们重新确定一个新的需求：

1、去空格

2、小数点最多4位，最少保留2位。

    1--->'1.00'；1.1--->'1.00'；1.12-->'1.12'；1.1234--->'1.1234'；

    1.12345--->'1.1235'

最终实现如下：

/*
  FM ：除空格  
  9999999.0099：允许小数点左边最大正数为7位，小数点右边最少2位，最多4位，且在第5位进行四舍五入
*/ 
Select TO_CHAR(123.0233,'FM9999999.0099') FROM DUAL