一个update的小故事

if object_id(‘tempdb..#TB‘) is not null
    drop table #TB
go

create table #TB
(
    ID int
)

insert into #TB (ID)
select 1
union all
select 2
union all
select 3
union all
select 4
union all
select 5

--代码1
declare @i int 
set @i = 1
while @i < 5
begin
    update #TB set ID = ID,@i = @i + 1
    select @i
end

--代码2
set @i = 1
while @i < 5
begin
    update #TB set ID = ID
　　 set @i = @i + 1
    select @i
end