将已有列改为自增列

  select   *   into   tmp   from   t   
  //将数据放入临时表
  alter   table   t   drop   column   id   
  alter   table   t   add   id   int   identity(1,1)   
  set   identity_insert   t   on   
  insert   into   t(id,col1,col2)   select   id,col1,col2   from   tmp
  //这里不能用*，要指定列才行   
  set   identity_insert   t   off   
  drop   table   tmp