oracle显示一个月的所有天数

效率高：

select to_date('200809','yyyymm')+(rownum-1) s_date from dual  
connect by rownum<=last_day(to_date('200809','yyyymm')) - to_date('200809','yyyymm') + 1

效率低：

select  
 to_date('200902','yyyymm')+(rownum-1) s_date    
 from all_tables  
 where rownum <=  
(  
 select last_day(to_date('200902','yyyymm')) - to_date('200902','yyyymm')+1 from dual  
 )