sql 树形递归查询

sql 树形递归查询：

with ProductClass(ClassId,ClassName) as
(    
select ClassId,ClassName from Classes where ClassId = 31281
union all
select c.ClassId,c.ClassName from Classes c inner join ProductClass parent on c.ParentClassId = parent.ClassId
)
select  c.ClassId, c.ClassName, m.ProductId, m.ProductName
from ProductClass c
 inner join Products m on c.ClassId = m.ClassId