oracle
--取现在时间
select sysdate from dual --2010-7-15 10:51:31
--前两天，默认以天为单位
select sysdate-2 from dual --2010-7-13 10:51:31
--前一小时
select sysdate-1/24 from dual --2010-7-15 9:51:31
--前两个月
select add_months(sysdate,-2) from dual --2010-5-15 10:51:31
--字符串转日期
select to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\') from dual --2010-7-15 10:51:31
select to_date(\'2010-7-15\',\'yyyy-mm-dd\') from dual --2010-7-15
--日期转字符串
select to_char(sysdate,\'yyyy\') from dual --2010
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'yyyy\') from dual --2010
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'year\') from dual --twenty ten
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'mm\') from dual --07
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'month\') from dual --7月
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'dd\') from dual --15
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'day\') from dual --星期四
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'hh24\') from dual --10
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'mi\') from dual --51
select to_char(to_date(\'2010-7-15 10:51:31\',\'yyyy-mm-dd hh24:mi:ss\'),\'ss\') from dual --31
--求时间差
select to_date(\'2010-07-14 9:12:35\',\'yyyy-mm-dd hh24:mi:ss\') -
to_date(\'2010-07-13 15:12:35\',\'yyyy-mm-dd hh24:mi:ss\') from dual --0.75，默认以天为单位
select (to_date(\'2010-07-14 9:12:35\',\'yyyy-mm-dd hh24:mi:ss\') -
to_date(\'2010-07-13 15:12:35\',\'yyyy-mm-dd hh24:mi:ss\'))*24 from dual --18，转化为小时
select (to_date(\'2010-07-14 9:12:35\',\'yyyy-mm-dd hh24:mi:ss\') -
to_date(\'2010-07-13 15:12:36\',\'yyyy-mm-dd hh24:mi:ss\'))*24 from dual --17.9997222222222，与分秒有关
--选出2010-7-13 15:30:00之后的新闻
select NewsId,NewsTitle from BS_News where CreateTime >= to_date(\'2010-7-13 15:30:00\',\'yyyy-mm-dd hh24:mi:ss\')
--选出2010-7-13 00:00:00之后的新闻
select NewsId,NewsTitle from BS_News where CreateTime >= to_date(\'2010-7-13 00:00:00\',\'yyyy-mm-dd hh24:mi:ss\')
--等价于：select NewsId,NewsTitle from BS_News where CreateTime >= to_date(\'2010-7-13\',\'yyyy-mm-dd\')
--选出2010.07.12的新闻
select NewsId,NewsTitle from BS_News where CreateTime between to_date(\'2010-07-12\',\'yyyy-mm-dd\') and to_date(\'2010-07-12
23:59:59\',\'yyyy-mm-dd hh24:mi:ss\')
sql
--取现在时间
select getdate() --2010-07-13 10:51:31.793
--前两天
select dateadd(dd,-2,getdate()) --2010-07-13 10:51:31.793
--前一小时
select dateadd(hh,-1,getdate()) --2010-07-15 9:51:31.793
--前两个月
select dateadd(mm,-2,getdate()) --2010-05-15 10:51:31.793
--字符串转日期
select cast(\'2010-07-15 10:51:31.793\' as datetime) --2010-07-15 10:51:31.793
--日期转字符串
select cast(getdate() as varchar(18)) --07 15 2010 10:51AM
select convert(varchar(18),getdate()) --07 15 2010 10:51AM
--转成更多字符串格式
Select convert(varchar(19),getdate(), 20) --2010-07-15 10:51:31
Select convert(varchar(10),getdate(), 111) --2010/07/15
--求时间差
--精确到年份，2010-2009=1，与月/日无关
select datediff(yyyy, \'2009-07-14\', \'2010-01-20\')
--精确到小时，11-9+24=26，与分/秒无关
select datediff(hh,\'2010-07-14 9:12:35.012\',\'2010-07-15 11:50:35.012\')
--类似的date-part单位还有mm-月，dd-日，mi-分钟，ss-秒，mi-毫秒
--选出2010-7-13 15:30:00之后的新闻
select NewsId,NewsTitle from BS_News where CreateTime >= cast(\'2010-7-13 15:30:00\' as datetime)
--选出2010-7-13 00:00:00之后的新闻
select NewsId,NewsTitle from BS_News where CreateTime >= cast(\'2010-7-13 00:00:00\' as datetime)
--等价于：select NewsId,NewsTitle from BS_News where CreateTime >= cast(\'2010-7-13\' as datetime)
--选出2010.07.12的新闻
select NewsId,NewsTitle from BS_News where CreateTime between cast(\'2010-07-12\' as datetime) and cast(\'2010-07-12 23:59:59\'
as datetime)