Get all parents for a child

问题:

I want to retrieve the parentid of an id, if that parentid has a parent again retrieve it, and so on. Kind of hierarchy table.

id----parentid
1-----1
5-----1
47894--5
47897--47894

am new to sql server and tried, some queries like:

with name_tree as 
(
   select id, parentid
   from Users
   where id = 47897 -- this is the starting point you want in your recursion
   union all
   select c.id, c.parentid
   from users c
   join name_tree p on p.id = c.parentid  -- this is the recursion
) 
select *
from name_tree;

It is giving me only one row. and also I want to insert these records into a temporary table variable. How can I do this. thanks in advance. sorry for asking the simple question(though not to me)

回答1:

Try this to get all parents of a child

;with name_tree as 
(
   select id, parentid
   from Users
   where id = 47897 -- this is the starting point you want in your recursion
   union all
   select C.id, C.parentid
   from Users c
   join name_tree p on C.id = P.parentid  -- this is the recursion
   -- Since your parent id is not NULL the recursion will happen continously.
   -- For that we apply the condition C.id<>C.parentid 
    AND C.id<>C.parentid 
) 
-- Here you can insert directly to a temp table without CREATE TABLE synthax
select *
INTO #TEMP
from name_tree
OPTION (MAXRECURSION 0)

SELECT * FROM #TEMP

Click here to view result

EDIT :

If you want to insert into a table variable, you can do something like:

-- Declare table varialbe
Declare @TABLEVAR table (id int ,parentid int)


;with name_tree as 
(
   select id, parentid
   from #Users
   where id = 47897 -- this is the starting point you want in your recursion
   union all
   select C.id, C.parentid
   from #Users c
   join name_tree p on C.id = P.parentid  -- this is the recursion
   -- Since your parent id is not NULL the recursion will happen continously.
   -- For that we apply the condition C.id<>C.parentid 
    AND C.id<>C.parentid 
) 
-- Here you can insert directly to table variable
INSERT INTO @TABLEVAR
select *
from name_tree
OPTION (MAXRECURSION 0)

SELECT * FROM @TABLEVAR

Click here to view result

回答2:

Your query is doing recursion but in opposite direction. So if you change starting point to:

where id = 1

then you will have user 1 and all his successors

回答3:

you didn't mention the desired output and input. However you can try like this,

Declare @t table (id int ,parentid int)
insert into @t
select 1,1 union all
select 5,1 union all
select 47894,5 union all
select 47897,47894 

;With CTE as
(
select * from @t where id=1
union all
Select a.* from @t a inner join cte b
 on b.id=a.parentid and
a.id<>b.id
)
select * from cte