请问以下句子如何改正？
select   item1
from  
(
select   item1,   ordering   =   CASE   WHEN   item2   IS   NULL   THEN   1   ELSE   0   END
from   tableA
order   by   ordering
)

------解决方案--------------------
select item1
from
(
select top 100 percent item1, ordering = CASE WHEN item2 IS NULL THEN 1 ELSE 0 END
from tableA
order by ordering
)a

------解决方案--------------------
select item1
from
(
select top 100 percent item1, ordering = CASE WHEN item2 IS NULL THEN 1 ELSE 0 END
from tableA
order by ordering
)a
------解决方案--------------------
(
select item1, ordering = CASE WHEN item2 IS NULL THEN 1 ELSE 0 END
from tableA
Where TableB.Item3 = TableA.Item3
order by ordering
)

--内有order by ，需要在select 后面加top ,所以会报错！
正确的为：

Update TableB
Set Item1 =
(
select TOP 1 item1
from
(
select top 100 percent item1, ordering = CASE WHEN item2 IS NULL THEN 1 ELSE 0 END
from tableA
Where TableB.Item3 = TableA.Item3
order by ordering
) a
)