寫oracle sql挺好玩

select count(count_date)
  from (select to_char(b.ich_dadate, 'yyyy-mm-dd') count_date
          from ic_trnl a
         inner join ic_trnh b on b.ich_sno = a.ich_sno
         where to_char(b.ich_dadate, 'yyyy-MM-dd') between '2012-08-01' and
               '2012-08-07'
         group by to_char(b.ich_dadate, 'yyyy-mm-dd'))

結果： 6


select count(distinct to_char(b.ich_dadate, 'yyyy-mm-dd')) count_date
  from ic_trnh b
 where to_char(b.ich_dadate, 'yyyy-MM-dd') between '2012-08-01' and
       '2012-08-07'
 group by to_char(b.ich_dadate, 'yyyy-mm-dd')
 
 結果： 6 個 1
        1
        1
        1
        1
        1
        1
 
 select count(distinct to_char(b.ich_dadate, 'yyyy-mm-dd')) count_date
  from ic_trnh b
 where to_char(b.ich_dadate, 'yyyy-MM-dd') between '2012-08-01' and '2012-08-07'

結果：6