(to_date、to_char) 用法总结
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 se