In Oracle, we can use the function CONNECT_BY_ISCYCLE to detect a cycle in Hierarchical Queries. I try to do the same in SQL Server. Is there a way to do this?
Thanks a lot!
Concatenate the records IDs / build a bitmap based on ROW_NUMBERs of the records and verify each new record against the list/bitmap
create table t (id int,pid int)
insert into t values (1,3),(2,1),(3,2)
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
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,
ID should be a sequence of numbers starting with 1.
If necessary generate it using ROW_NUMBER.
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
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