1. 日期和字符转换函数用法（to_date,to_char）
select to_char(sysdate,\'yyyy-mm-dd hh24:mi:ss\') as nowTime from dual; //日期转化为字符串
select to_char(sysdate,\'yyyy\') as nowYear from dual; //获取时间的年
select to_char(sysdate,\'mm\') as nowMonth from dual; //获取时间的月
select to_char(sysdate,\'dd\') as nowDay from dual; //获取时间的日
select to_char(sysdate,\'hh24\') as nowHour from dual; //获取时间的时
select to_char(sysdate,\'mi\') as nowMinute from dual; //获取时间的分
select to_char(sysdate,\'ss\') as nowSecond from dual; //获取时间的秒
2. 字符串和时间互转
select to_date(\'2004-05-07 13:23:44\',\'yyyy-mm-dd hh24:mi:ss\') from dual
select to_char( to_date(222,\'J\'),\'Jsp\') from dual //显示Two Hundred Twenty-Two
3.求某天是星期几
select to_char(to_date(\'2002-08-26\',\'yyyy-mm-dd\'),\'day\') from dual; //星期一
select to_char(to_date(\'2002-08-26\',\'yyyy-mm-dd\'),\'day\',
\'NLS_DATE_LANGUAGE = American\') from dual; // monday
//设置日期语言
ALTER SESSION SET NLS_DATE_LANGUAGE=\'AMERICAN\';
//也可以这样
TO_DATE (\'2002-08-26\', \'YYYY-mm-dd\', \'NLS_DATE_LANGUAGE = American\')
4. 两个日期间的天数
select floor(sysdate - to_date(\'20020405\',\'yyyymmdd\')) from dual
5. 时间为null的用法
select id, active_date from table1
UNION
select 1, TO_DATE(null) from dual; //注意要用TO_DATE(null)
6.月份差
a_date between to_date(\'20011201\',\'yyyymmdd\') and to_date(\'20011231\',\'yyyymmdd\')
//那么12月31号中午12点之后和12月1号的12点之前是不包含在这个范围之内的。
//所以，当时间需要精确的时候，觉得to_char还是必要的
7. 日期格式冲突问题
输入的格式要看你安装的ORACLE字符集的类型, 比如: US7ASCII, date格式的类型就是: \'01-Jan-01\'
alter system set NLS_DATE_LANGUAGE = American
alter session set NLS_DATE_LANGUAGE = American
//或者在to_date中写
select to_char(to_date(\'2002-08-26\',\'yyyy-mm-dd\'),
\'day\',\'NLS_DATE_LANGUAGE = American\') from dual;
//注意我这只是举了NLS_DATE_LANGUAGE，当然还有很多，可查看
select * from nls_session_parameters
select * from V$NLS_PARAMETERS
8.查询特殊条件天数
select count(*)
from ( select rownum-1 rnum
from all_objects
where rownum <= to_date(\'2002-02-28\',\'yyyy-mm-dd\') - to_date(\'2002-
02-01\',\'yyyy-mm-dd\')+1
)
where to_char( to_date(\'2002-02-01\',\'yyyy-mm-dd\')+rnum-1, \'D\' )
not in ( \'1\', \'7\' )
//查找2002-02-28至2002-02-01间除星期一和七的天数
//在前后分别调用DBMS_UTILITY.GET_TIME, 让后将结果相减(得到的是1/100秒, 而不是毫秒)
9. 查找月份
select months_between(to_date(\'01-31-1999\',\'MM-DD-YYYY\'),
to_date(\'12-31-1998\',\'MM-DD-YYYY\')) "MONTHS" FROM DUAL;
//结果为：1
select months_between(to_date(\'02-01-1999\',\'MM-DD-YYYY\'),
to_date(\'12-31-1998\',\'MM-DD-YYYY\')) "MONTHS" FROM DUAL;
//结果为：1.03225806451613
10. Next_day的用法
Next_day(date, day)
Monday-Sunday, for format code DAY
Mon-Sun, for format code DY
1-7, for format code D
11.获得小时数
//extract()找出日期或间隔值的字段值
SELECT EXTRACT(HOUR FROM TIMESTAMP \'2001-02-16 2:38:40\') from offer
select sysdate ,to_char(sysdate,\'hh\') from dual;
SYSDATE TO_CHAR(SYSDATE,\'HH\')
-------------------- ---------------------
2003-10-13 19:35:21 07
select sysdate ,to_char(sysdate,\'hh24\') from dual;
SYSDATE TO_CHAR(SYSDATE,\'HH24\')
-------------------- -----------------------
2003-10-13 19:35:21 19
12.年月日的处理
SELECT
older_date,
newer_date,
years,
months,
ABS (
TRUNC (
newer_date - ADD_MONTHS (older_date, years * 12 + months)
)
) days
FROM
(
SELECT
TRUNC (
MONTHS_BETWEEN (newer_date, older_date) / 12
) YEARS,
MOD (
TRUNC (
MONTHS_BETWEEN (newer_date, older_date)
),
12
) MONTHS,
newer_date,
older_date
FROM
(
SELECT
hiredate older_date,
ADD_MONTHS (hiredate, ROWNUM) + ROWNUM newer_date
FROM
emp
)
)
13.处理月份天数不定的办法
select to_char(add_months(last_day(sysdate) +1, -2), \'yyyymmdd\'),last_day(sysdate) from dual
14.找出今年的天数
select add_months(trunc(sysdate,\'year\'), 12) - trunc(sysdate,\'year\') from dual
//闰年的处理方法
to_char( last_day( to_date(\'02\' | | :year,\'mmyyyy\') ), \'dd\' )
//如果是28就不是闰年
15.yyyy与rrrr的区别
YYYY99 TO_C
------- ----
yyyy 99 0099
rrrr 99 1999
yyyy 01 0001
rrrr 01 2001
16.不同时区的处理
select to_char( NEW_TIME( sysdate, \'GMT\',\'EST\'), \'dd/mm/yyyy hh:mi:ss\') ,
sysdate from dual;
17. 5秒钟一个间隔
Select TO_DATE(FLOOR(TO_CHAR(sysdate,\'SSSSS\')/300) * 300,\'SSSSS\') ,
TO_CHAR(sysdate,\'SSSSS\') from dual
//2002-11-1 9:55:00 35786
//SSSSS表示5位秒数
18.一年的第几天
select TO_CHAR(SYSDATE,\'DDD\'),sysdate from dual
//310 2002-11-6 10:03:51
19.计算小时,分,秒,毫秒
SELECT
Days,
A,
TRUNC (A * 24) Hours,
TRUNC (A * 24 * 60 - 60 * TRUNC(A * 24)) Minutes,
TRUNC (
A * 24 * 60 * 60 - 60 * TRUNC (A * 24 * 60)
) Seconds,
TRUNC (
A * 24 * 60 * 60 * 100 - 100 * TRUNC (A * 24 * 60 * 60)
) mSeconds
FROM
(
SELECT
TRUNC (SYSDATE) Days,
SYSDATE - TRUNC (SYSDATE) A
FROM
dual
) SELECT
*
FROM
tabname
ORDER BY
DECODE (MODE, \'FIFO\', 1 ,- 1) * TO_CHAR (rq, \'yyyymmddhh24miss\')
// floor((date2-date1) /365) 作为年
// floor((date2-date1, 365) /30) 作为月
// d(mod(date2-date1, 365), 30)作为日.
20.next_day函数
//返回下个星期的日期,day为1-7或星期日-星期六,1表示星期日
next_day(sysdate,6)是从当前开始下一个星期五。后面的数字是从星期日开始算起。
// 1 2 3 4 5 6 7
//日 一 二 三 四 五 六
select (sysdate-to_date(\'2003-12-03 12:55:45\',\'yyyy-mm-dd hh24:mi:ss\'))*24*60*60 from dual
//日期 返回的是天 然后 转换为ss
21,round[舍入到最接近的日期](day:舍入到最接近的星期日)
select sysdate S1,
round(sysdate) S2 ,
round(sysdate,\'year\') YEAR,
round(sysdate,\'month\') MONTH ,
round(sysdate,\'day\') DAY from dual
22,trunc[截断到最接近的日期,单位为天] ,返回的是日期类型
select sysdate S1,
trunc(sysdate) S2, //返回当前日期,无时分秒
trunc(sysdate,\'year\') YEAR, //返回当前年的1月1日,无时分秒
trunc(sysdate,\'month\') MONTH , //返回当前月的1日,无时分秒
trunc(sysdate,\'day\') DAY //返回当前星期的星期天,无时分秒
from dual
23,返回日期列表中最晚日期
select greatest(\'01-1月-04\',\'04-1月-04\',\'10-2月-04\') from dual
24.计算时间差
注:oracle时间差是以天数为单位,所以换算成年月,日
select floor(to_number(sysdate-to_date(\'2007-11-02 15:55:03\',
\'yyyy-mm-dd hh24:mi:ss\'))/365) as spanYears from dual //时间差-年
select ceil(moths_between(sysdate-to_date(\'2007-11-02 15:55:03\',
\'yyyy-mm-dd hh24:mi:ss\'))) as spanMonths from dual //时间差-月
select floor(to_number(sysdate-to_date(\'2007-11-02 15:55:03\',
\'yyyy-mm-dd hh24:mi:ss\'))) as spanDays from dual //时间差-天
select floor(to_number(sysdate-to_date(\'2007-11-02 15:55:03\',
\'yyyy-mm-dd hh24:mi:ss\'))*24) as spanHours from dual //时间差-时
select floor(to_number(sysdate-to_date(\'2007-11-02 15:55:03\',
\'yyyy-mm-dd hh24:mi:ss\'))*24*60) as spanMinutes from dual //时间差-分
select floor(to_number(sysdate-to_date(\'2007-11-02 15:55:03\',
\'yyyy-mm-dd hh24:mi:ss\'))*24*60*60) as spanSeconds from dual //时间差-秒
25.更新时间
//oracle时间加减是以天数为单位,设改变量为n,所以换算成年月,日
select to_char(sysdate,\'yyyy-mm-dd hh24:mi:ss\'),
to_char(sysdate+n*365,\'yyyy-mm-dd hh24:mi:ss\') as newTime from dual //改变时间-年
select to_char(sysdate,\'yyyy-mm-dd hh24:mi:ss\'),
add_months(sysdate,n) as newTime from dual //改变时间-月
select to_char(sysdate,\'yyyy-mm-dd hh24:mi:ss\'),
to_char(sysdate+n,\'yyyy-mm-dd hh24:mi:ss\') as newTime from dual //改变时间-日
select to_char(sysdate,\'yyyy-mm-dd hh24:mi:ss\'),
to_char(sysdate+n/24,\'yyyy-mm-dd hh24:mi:ss\') as newTime from dual //改变时间-时
select to_char(sysdate,\'yyyy-mm-dd hh24:mi:ss\'),
to_char(sysdate+n/24/60,\'yyyy-mm-dd hh24:mi:ss\') as newTime from dual //改变时间-分
select to_char(sysdate,\'yyyy-mm-dd hh24:mi:ss\'),
to_char(sysdate+n/24/60/60,\'yyyy-mm-dd hh24:mi:ss\') as newTime from dual //改变时间-秒
26.查找月的第一天,最后一天
SELECT Trunc(Trunc(SYSDATE, \'MONTH\') - 1, \'MONTH\') First_Day_Last_Month,
Trunc(SYSDATE, \'MONTH\') - 1 / 86400 Last_Day_Last_Month,
Trunc(SYSDATE, \'MONTH\') First_Day_Cur_Month,
LAST_DAY(Trunc(SYSDATE, \'MONTH\')) + 1 - 1 / 86400 Last_Day_Cur_Month
FROM dual;