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') = TO_CHAR(SYSDATE,'YYYY')
GROUP BY TO_CHAR(T.MODIFIEDTIME,'IW'),TO_CHAR(T.MODIFIEDTIME,'YYYY')   --根据周数来分组
ORDER BY TO_CHAR(T.MODIFIEDTIME,'YYYY'),TO_CHAR(T.MODIFIEDTIME,'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') = TO_CHAR(SYSDATE,'YYYY')

GROUP BY 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,'YYYY') YEAR,TO_CHAR(T.MODIFIEDTIME,'Q') 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,'Q'),TO_CHAR(T.MODIFIEDTIME,'YYYY')   --根据每年季度来分组

ORDER BY TO_CHAR(T.MODIFIEDTIME,'YYYY'),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,'YYYY') YEAR,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