sql-server - 有没有办法在 SQL Server 的分层查询中检测循环？

Question

在 Oracle 中，我们可以使用函数 CONNECT_BY_ISCYCLE检测层次查询中的循环。我尝试在 SQL Server 中做同样的事情。有没有办法做到这一点？

非常感谢!

Answer 1

连接记录 ID/基于记录的 ROW_NUMBER 构建位图，并根据列表/位图验证每个新记录

create table t (id int,pid int)
insert into t values (1,3),(2,1),(3,2)

列表

识别周期

with cte (id,pid,list,is_cycle) 
as
(
    select      id,pid,',' + cast (id as varchar(max))  + ',',0
    from        t
    where       id = 1

    union all

    select      t.id,t.pid,cte.list + cast (t.id as varchar(10)) +  ',' ,case when cte.list like '%,' + cast (t.id as varchar(10)) + ',%' then 1 else 0 end
    from        cte join t on t.pid = cte.id
    where       cte.is_cycle = 0
)
select      *
from        cte
where       is_cycle = 1

id  pid list        is_cycle
--  --- ----        --------
1   3   ,1,2,3,1,   1

用循环遍历完整图

with cte (id,pid,list) 
as
(
    select      id,pid,',' + cast (id as varchar(max))  + ','
    from        t
    where       id = 1

    union all

    select      t.id,t.pid,cte.list + cast (t.id as varchar(10)) +  ',' 
    from        cte join t on t.pid = cte.id
    where       cte.list not like '%,' + cast (t.id as varchar(10)) + ',%'
)
select      *
from        cte

id  pid list
1   3   ,1,
2   1   ,1,2,
3   2   ,1,2,3,

位图

ID 应该是一个以 1 开头的数字序列。
如有必要，请使用 ROW_NUMBER 生成它。

识别周期

with cte (id,pid,bitmap,is_cycle) 
as
(
    select      id,pid,cast (power(2,id-1) as varbinary(max)) ,0
    from        t
    where       id = 1

    union all

    select      t.id,t.pid,cast (cte.bitmap|power(2,t.id-1) as varbinary(max)),case when cte.bitmap & power(2,t.id-1) > 0 then 1 else 0 end
    from        cte join t on t.pid = cte.id
    where       cte.is_cycle = 0
)
select      *
from        cte
where       is_cycle = 1

id  pid bitmap      is_cycle
1   3   0x00000007  1

用循环遍历完整图

with cte (id,pid,bitmap) 
as
(
    select      id,pid,cast (power(2,id-1) as varbinary(max))
    from        t
    where       id = 1

    union all

    select      t.id,t.pid,cast (cte.bitmap|power(2,t.id-1) as varbinary(max))
    from        cte join t on t.pid = cte.id
    where       cte.bitmap & power(2,t.id-1) = 0
)
select      *
from        cte

id  pid bitmap
1   3   0x00000001
2   1   0x00000003
3   2   0x00000007