Oracle 中的周、月、日历的查询实现

/**
1. 周
一年总共只有53周
有两种情况，在于当年第一周的第一天和最后一天怎么算，后面只需加上7天就是一周，类推
a. 第一种，周日为第一天 ，周六为最后一天
b. 第二种，周一为第一天，周日为最后一天
*/
-- a. 第一种
SELECT LEVEL 周次,
       (Trunc(SYSDATE, 'yyyy') - 7) + (7 - To_Char(Trunc(SYSDATE, 'yyyy'), 'd') + 1) +
       (LEVEL - 1) * 7 当周第一天,
       (Trunc(SYSDATE, 'yyyy') - 7) + (7 - To_Char(Trunc(SYSDATE, 'yyyy'), 'd') + 1) +
       (LEVEL - 1) * 7 + 6 当周最后一天
  FROM dual
CONNECT BY LEVEL <= 53;


-- b. 第二种
select '第' || level || '周' as week_no,
       next_day(trunc(sysdate, 'yyyy'), '星期一') + (level - 1) * 7 as monday,
       next_day(trunc(sysdate, 'yyyy'), '星期日') + (level - 1) * 7 as sunday
  from dual
connect by level <= 53;



/**
2、月份
查询当年每个月的起止时间
*/
select aa as monNum,
       to_date(mon, 'yyyymmdd') as firstDay,
       LAST_DAY(to_date(mon, 'yyyymmdd')) as lastDay
  from (select to_char(sysdate, 'yyyy') || to_char(aa, '09') || '01' mon, aa
          from (select 1 aa
                  from dual
                union
                select 2 aa
                  from dual
                union
                select 3 aa
                  from dual
                union
                select 4 aa
                  from dual
                union
                select 5 aa
                  from dual
                union
                select 6 aa
                  from dual
                union
                select 7 aa
                  from dual
                union
                select 8 aa
                  from dual
                union
                select 9 aa
                  from dual
                union
                select 10 aa
                  from dual
                union
                select 11 aa
                  from dual
                union
                select 12 aa from dual));



/**
3、日历
以下查询可输入年份
*/
select case
         when (new_yweek = min(new_yweek) over(partition by mon order by new_yweek)) then
          mon_name
         else
          null
       end as month,  -- 月份
       new_yweek as yweek,  -- 一年中的第几周
       row_number() over(partition by mon order by new_yweek) as mweek,  -- 每个月中的周顺序
       sum(decode(wday, '1', mday, null)) as Sunday,
       sum(decode(wday, '2', mday, null)) as Monday,
       sum(decode(wday, '3', mday, null)) as tuesday,
       sum(decode(wday, '4', mday, null)) as Wednesday,
       sum(decode(wday, '5', mday, null)) as Thursday,
       sum(decode(wday, '6', mday, null)) as Friday,
       sum(decode(wday, '7', mday, null)) as Saturday
  from (select dayofyear as everyday,
               to_char(dayofyear, 'mm') as mon,
               to_char(dayofyear, 'Month') as mon_name,
               to_char(dayofyear, 'w') as mweek,
               to_char(dayofyear, 'ww') as yweek,
               case
                 when (to_char(to_date(&year || '0101', 'yyyymmdd'), 'd') > '1') and
                      (to_char(dayofyear, 'd') < to_char(to_date(&year || '0101', 'yyyymmdd'), 'd')) then
                  to_char(to_char(dayofyear, 'ww') + 1, 'fm00')
                 else
                  to_char(dayofyear, 'ww')
               end as new_yweek,
               to_char(dayofyear, 'd') as wday,
               to_char(dayofyear, 'dd') as mday
          from (select to_date(&year || '0101', 'yyyymmdd') + level - 1 as dayofyear
                  from dual
                connect by level <= to_char(to_date(&year || '1231', 'yyyymmdd'), 'ddd')))
 group by mon, mon_name, new_yweek;