sql-server-2008 - 如何在查询中使用递归获取父级的所有子级，然后获取其子级

Question

我的结构是这样的:

<Unit>
  <SubUnit1>
           <SubSubUnit1/>
           <SubSubUnit2/>
           ...
           <SubSubUnitN/>
  </SubUnit1/>
  <SubUnit2>
           <SubSubUnit1/>
           <SubSubUnit2/>
           ...
           <SubSubUnitN/>
  </SubUnit2/>
  ...
  <SubUnitN>
           <SubSubUnit1/>
           <SubSubUnit2/>
           ...
           <SubSubUnitN/>
  </SubUnitN/>
</Unit>

该结构有 3 个级别:主单元、子单元和子子单元。

我想按 UnitId 选择所有子项。
如果我按单位搜索，我必须获取所有树。
如果我按 SubUnit1 搜索，则必须获取 SubUnit1 以及 SubUnit1 的所有子级。
如果我搜索 SubSubUnit2，我必须得到它本身。

这是我的尝试:

with a(id, parentid, name)
as (
select id, parentId, name
   from customer a
   where parentId is null 
union all
   select a.id, a.parentid, a.Name
   from customer
     inner join a on customer.parentId = customer.id
    )
select parentid, id, name 
from customer pod
where pod.parentid in (
select id
from customer grbs
where grbs.parentid in (
select id
from customer t
where t.parentid = @UnitId
))
union 
select parentid, id, name
from customer grbs
where grbs.parentid in (
select id
from customer t
where t.parentid = @UnitId
)
union
select parentid, id, name
from customer c
where c.Id = @UnitId
order by parentid, id

我使用了 3 个联合词，虽然不太好，但很有效。 Case 结构有 N 个级别，我如何才能得到正确的结果？

Answer 1

DECLARE @Id int = your_UnitId
;WITH cte AS 
 (
  SELECT a.Id, a.parentId, a.name
  FROM customer a
  WHERE Id = @Id
  UNION ALL
  SELECT a.Id, a.parentid, a.Name
  FROM customer a JOIN cte c ON a.parentId = c.id
  )
  SELECT parentId, Id, name
  FROM cte

演示 SQLFiddle