方法一:
select identity(int,1,1) as id,users into #t from mytable
delete from mytable
insert into mytable select * from #t
drop table #t
select identity(int,1,1) as id,users into #t from mytable
delete from mytable
insert into mytable select * from #t
drop table #t
update mytable set id=(select count(*) from mytable a where a.users<=b.users) from mytable b