SQL Server 通过with as方法查询树型结构

--指定列
with withTmp1 (code,cName)
as
(
 select id,Name from ClassUnis
)
select  from withTmp1
--自动列
with withTmp2 
as
(
 select  from ClassUnis
 where Author = 'system'
)
select  from withTmp2

with tree as(
 --0 as Level 定义树的层级,从0开始
 select ,0 as Level 
 from ClassUnis
 where ParentId is null
 union all
 --t.Level + 1每递归一次层级递增
 select c.,t.Level + 1 
 from ClassUnis c,tree t
 where c.ParentId = t.ID
 --from ClassUnis c inner join tree t on c.ParentId = t.ID
)
select  from tree where Author not like'%/%'

with tree as(
 select ,0 as Level from ClassUnis where ParentId is null
 union all
 select c.,t.Level + 1 from ClassUnis c,tree t where c.ParentId = t.ID
)
select  from tree where Author not like'%/%' 
option(maxrecursion 1)