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

--创建表 Test

CTEATE TABLE TEST(

ID NUMBER NOT NULL,

MODIFIEDTIME DATE NOT NULL

）

--按天统计

SELECT TO_CHAR(T.MODIFIEDTIME,'YYYY-MM-DD') TIME,COUNT(*) COUNT

FROM TEST T

--这里可加查询条件 WHERE TO_CHAR(T.MODIFIEDTIME,'YYYY') = TO_CHAR(SYSDATE,'YYYY')

GROUP BY TO_CHAR(T.MODIFIEDTIME,'YYYY-MM-DD') --根据日期来分组

ORDER BY TO_CHAR(T.MODIFIEDTIME,'YYYY-MM-DD') ASC NULLS LAST --根据日期排序

--按周统计
SELECT TO_CHAR(T.MODIFIEDTIME,'YYYY') YEAR,TO_CHAR(T.MODIFIEDTIME,'IW') TIME,COUNT(*) COUNT
FROM TEST T
--这里可加查询条件 WHERE TO_CHAR(T.MODIFIEDTIME,'YYYY')
GROUP BY TO_CHAR(T.MODIFIEDTIME,'IW'),'YYYY') --根据周数来分组
ORDER BY TO_CHAR(T.MODIFIEDTIME,'YYYY'),'IW') ASC NULLS LAST --根据周数来排序

--按月统计

SELECT TO_CHAR(T.MODIFIEDTIME,'YYYY-MM') TIME,COUNT(*) COUNT

FROM TEST T

--这里可加查询条件 WHERE TO_CHAR(T.MODIFIEDTIME,'YYYY-MM') --根据月份来分组

ORDER BY TO_CHAR(T.MODIFIEDTIME,'YYYY-MM') ASC NULLS LAST--根据月份来排序

--按季度统计
SELECT TO_CHAR(T.MODIFIEDTIME,'Q') TIME,'YYYY')
GROUP BY TO_CHAR(T.MODIFIEDTIME,'Q'),'YYYY') --根据每年季度来分组

ORDER BY TO_CHAR(T.MODIFIEDTIME,'Q') ASC NULLS LAST --根据每年季度来排序

--按年统计
SELECT TO_CHAR(T.MODIFIEDTIME,COUNT(*) COUNT
FROM TEST T
--这里可加查询条件
GROUP BY TO_CHAR(T.MODIFIEDTIME,'YYYY') --根据年份来分组

ORDER BY TO_CHAR(T.MODIFIEDTIME,'YYYY') ASC NULLS LAST --根据年份来排序