sqlserver中 First day 和 Last day的实现

   --LAST_DAY
   select cast(convert(varchar(7),dateadd(mm,1,'2012-02-04'),120) + '-01' as datetime) - 1  "LAST_DAY";
   
   select DATEADD(mm, DATEDIFF(mm, 0, '2012-02-04')+1, 0)-1 "LAST_DAY";
    
   --First Day
   select cast(convert(varchar(7),'2012-02-04',120) + '-01' as datetime) "First Day";
   
   select DATEADD(mm, DATEDIFF(mm, 0, '2012-02-04'), 0)  "First Day";