日期处理常用函数
sysdate:当前日期和时间;to_char():将数值型或日期型转换为字符型;to_date():日期转换函数,例:to_date(‘2017-09-27 10:00:00’, ‘yyyy-mm-dd hh24:mi:ss’);last_day(sysdate):返回日期所在月的最后一天;trunc(number[,decimals]):指定元素格式截去一部分日期值;add_months(D,N):返回日期D加N月后对应的日期时间,N为正时则表示D之后;N为负时则表示为D之前;N为小数则会自动先删除小数部分,而用整数部分;
decode(条件,值1,翻译值1,值2,翻译值2,…值n,翻译值n,缺省值):根据条件返回相应的值;ceil(n):取大于等于数值n的最小整数;floor(n):取小于等于数值n的最大整数;dbtimezone():返回时区;next_day(data,char):返回日期date的下一个星期几(char)的日期……
常见操作
select sysdate from dual;
select to_char(sysdate,'YYYYMMDD HH24:MI:SS W') from dual;
select to_char(sysdate,'w') from dual;
select to_char(sysdate,'d') from dual;
select to_char(sysdate,'yyyy') from dual;
select to_char(sysdate,'q') from dual;
select to_char(sysdate,'mm') from dual;
select to_char(sysdate,'dd') from dual;
select to_char(sysdate,'ddd') from dual;
select to_char(sysdate,'ww') from dual;
select to_char(sysdate,'w') from dual;
select to_char(sysdate,'day') from dual;
select to_char(sysdate,'hh') from dual;
select to_char(sysdate,'hh24') from dual;
select to_char(sysdate,'MI') from dual;
select to_char(sysdate,'ss') from dual;
select trunc(sysdate) from dual;
select trunc(sysdate)+0.99999 from dual;
select trunc(sysdate)+1/24 from dual;
select trunc(sysdate)+7/24 from dual;
select trunc(sysdate+1) from dual;
select trunc(sysdate)+1 from dual;
select trunc(sysdate,'mm') from dual;
select trunc(add_months(sysdate, 1),'mm') from dual;
select last_day(sysdate) from dual;
select last_day(trunc(sysdate)) from dual;
select trunc(last_day(sysdate)) from dual;
select trunc(add_months(sysdate,1),'mm') - 1 from dual;
select trunc(sysdate,'yyyy')+ rn -1 date0 from
(select rownum rn from all_objects
where rownum<366);
select add_months(sysdate,24) from dual;
select decode(to_char(last_day(trunc(sysdate,'y')+31),'dd'),'29','闰年','平年') from dual;
select decode(to_char(last_day(trunc(add_months(sysdate,24),'y')+31),'dd'),'29','闰年','平年') from dual;
select ceil(to_number(to_char(sysdate,'mm'))/3) from dual;
案例
根据时间以及用户id计算该用户本周、本日、本月记录的数据
select y.create_by,count(y.create_date),u.name from test y,sys_user u
where to_date(y.create_date)=to_date(sysdate) and y.create_by=u.id
group by y.create_by,u.name;
select create_by,count(create_date)
from test
where to_date(create_date)>=to_date(sysdate-to_number(to_char(sysdate-1,'D')+1)) and slzt='1'
group by create_by;
select to_char(create_date,'yyyy-mm'),create_by,count(create_date) from test
where to_date(create_date)>=to_date(trunc(sysdate,'mm')) and to_date(create_date)<=to_date(last_day(sysdate))
group by to_char(create_date,'yyyy-mm'),create_by;