TSQL 类别树的问题答案

【问题标题】：TSQL A problem with categories treeTSQL 类别树的问题
【发布时间】：2010-12-03 11:39:29
【问题描述】：

我遇到了递归 CTE 查询的问题

假设我有那个类别树（类别表）

在我的 CTE 查询中，我搜索 1 类别的所有子项：（该查询工作正常）

    with mq as
    (
        select c.Id as parent, c.Id as child 
            from dbo.Category c 
            where c.Id = 1
              union all
                select q.child, c.Id
                from mq q
                    inner join dbo.Category c on q.child = c.IdParentCategory
    )

输出

然后，我想得到那个没有孩子的类别 ID：类别9,10,12,14,15

with mq as
    (
        select c.Id as parent, c.Id as child 
        from dbo.Category c 
        where c.Id = 1
            union all
                select q.child, c.Id
                from mq q
                    inner join dbo.Category c on q.child = c.IdParentCategory
                where child in 
                (
                    select c1.Id
                    from  dbo.Category c1
                    where not exists(select c2.Id 
                                     from dbo.Category c2 
                                     where c2.Id = c1.IdParentCategory)
                ) 
    )

但输出错误：

为什么？任何想法都会有所帮助！

如果我将查询与 CTE 分开，一切正常

declare @tab table
(parent int, child int);

insert into @tab
        select * from mq

    delete from @tab
    where child  in (
        select c1.parent
        from @tab c1
        where not exists(select c2.parent from @tab c2 where c2.parent = c1.child)
    )

【问题讨论】：

标签： tsql recursion common-table-expression

【解决方案1】：

with mq as
(
    select c.Id as parent, c.Id as child 
        from dbo.Category c 
        where c.Id = 1
          union all
            select q.child, c.Id
            from mq q
                inner join dbo.Category c on q.child = c.IdParentCategory
)
select child from mq where child not in (select parent from mq)

似乎会给出你想要的输出——事实上你对问题的描述几乎就是这种形式。

【讨论】：