I have table with such structure.
ElementId | ParentId
-------------------
1 | NULL
2 | 1
3 | 2
4 | 3
Let say current element has Id 4. I want to select all parent ids.
Result should be: 3, 2, 1
How I can do it? DB is MSSQL
You can use recursive queries for this: http://msdn.microsoft.com/en-us/library/aa175801(SQL.80).aspx
You can use it like this:
with Hierachy(ElementID, ParentID, Level) as (
select ElementID, ParentID, 0 as Level
from table t
where t.ElementID = X -- insert parameter here
union all
select t.ElementID, t.ParentID, th.Level + 1
from table t
inner join Hierachy th
on t.ParentId = th.ElementID
)
select ElementID, ParentID
from Hierachy
where Level > 0
I think it might be easiest to do the following:
while parent != NULL
get parent of current element
I can't think of any way of doing this in plain SQL that wouldn't cause issues on larger databases.
if you want pure sql try:
select ParentId from myTable Desc
that would work in mysql... you might need to modify the Desc (sort in descending order) part
Related
I have a table with applications and table with messages. Applications has hierarchical structure, e.g each application has a parent. And I have a table with messages. Each message has a key and an application id. I want to be able to select message by it's key. If it's found for current application then return it, if no then try to find it with parent id.
Apps table:
id | name | parentId
--------------------
1 |parent| NULL
2 |child | 1
Msg table:
key | text | app
-------------------------------------------------
overriden.system.msg | some text | 1
parent.msg | parent txt | 1
overriden.system.msg | overriden text | 2
So if I'm in the child app(2) on key overriden.system.msg I want to get overriden text. On key parent.msg I want to get parent txt. I know that it must be done with cte, but I have very little expirience with sql and cte is mind-blowing for me right now. Could you please provide working query for this situation? Or maybe you have a better vision how to achieve such functionality without recursion?
The above should work fine:
with app_tree (id, app, lvl) as
( select id , parentID , 0
from Apps
where id = 2
union all
select t.app, a.parentID, t.lvl + 1 from
Apps a
join app_tree t
on t.app = a.id ),
all_msg as (
select key, text,
row_number() over ( partition by key order by lvl) overrideLevel
from app_tree a
join msg m
on m.app = a.id )
select * from all_msg where
overrideLevel =1
It returns:
KEY TEXT
-------------------------------------
overriden.system.msg overriden text
parent.msg parent txt
First it gets the list of all applications for specified id using recursive query with parentid. After that it gets a list of all functions for all applications and generates increasing numbers for the same keys basing on the level. At the end it just takes the first possible level and ignore all parent's levels for the same key.
Mb it will help you:
with app (id, name, parent_id) as
(select 1, 'parent', null from dual union all
select 2, 'child', 1 from dual)
,msg (key, text, app) as
(select 'overriden.system.msg', 'some text', 1 from dual union all
select 'parent.msg', 'parent txt', 1 from dual union all
select 'overriden.system.msg', 'overriden text', 2 from dual)
select key
,max(text) keep (dense_rank last order by nvl2(text,level,0)) msg
from
(select *
from app a
join msg m on (a.id = m.app)) v
start with v.parent_id is null
connect by prior v.id = v.parent_id and prior v.key = v.key
group by key
Is there any way to send a recursive query in SQL?
Given the end node id, I need all the rows up to the root node (which has parentid = NULL) ordered by level. E.g. if I have something like:
nodeid | parentid
a | NULL
b | a
c | b
after querying for end_node_id = c, I'd get something like:
nodeid | parentid | depth
a | NULL | 0
b | a | 1
c | b | 2
(Instead of the depth I can also work with the distance to the given end node)
The only (and obvious) way I could come up with is doing a single query per row until I reach the parent node.
Is there a more efficient way of doing it?
If you are using mssql 2005+ you can do this:
Test data:
DECLARE #tbl TABLE(nodeId VARCHAR(10),parentid VARCHAR(10))
INSERT INTO #tbl
VALUES ('a',null),('b','a'),('c','b')
Query
;WITH CTE
AS
(
SELECT
tbl.nodeId,
tbl.parentid,
0 AS Depth
FROM
#tbl as tbl
WHERE
tbl.parentid IS NULL
UNION ALL
SELECT
tbl.nodeId,
tbl.parentid,
CTE.Depth+1 AS Depth
FROM
#tbl AS tbl
JOIN CTE
ON tbl.parentid=CTE.nodeId
)
SELECT
*
FROM
CTE
Ended up with the following solutions (where level is the distance to the end node)
Oracle, using hierarchical queries (thanks to the info provided by #Mureinik):
SELECT IDCATEGORY, IDPARENTCATEGORY, LEVEL
FROM TNODES
START WITH IDCATEGORY=122
CONNECT BY IDCATEGORY = PRIOR IDPARENTCATEGORY;
Example using a view so it boils down to a single standard SQL query (requires >= 10g):
CREATE OR REPLACE VIEW VNODES AS
SELECT CONNECT_BY_ROOT IDCATEGORY "IDBRANCH", IDCATEGORY, IDPARENTCATEGORY, LEVEL AS LVL
FROM TNODES
CONNECT BY IDCATEGORY = PRIOR IDPARENTCATEGORY;
SELECT * FROM VNODES WHERE IDBRANCH = 122 ORDER BY LVL ASC;
http://sqlfiddle.com/#!4/18ba80/3
Postgres >= 8.4, using a WITH RECURSIVE Common Table Expression query:
WITH RECURSIVE BRANCH(IDPARENTCATEGORY, IDCATEGORY, LEVEL) AS (
SELECT IDPARENTCATEGORY, IDCATEGORY, 1 AS LEVEL FROM TNODES WHERE IDCATEGORY = 122
UNION ALL
SELECT p.IDPARENTCATEGORY, p.IDCATEGORY, LEVEL+1
FROM BRANCH pr, TNODES p
WHERE p.IDCATEGORY = pr.IDPARENTCATEGORY
)
SELECT IDCATEGORY,IDPARENTCATEGORY, LEVEL
FROM BRANCH
ORDER BY LEVEL ASC
Example using a view so it boils down to a single standard SQL query:
CREATE OR REPLACE VIEW VNODES AS
WITH RECURSIVE BRANCH(IDBRANCH,IDPARENTCATEGORY,IDCATEGORY,LVL) AS (
SELECT IDCATEGORY AS IDBRANCH, IDPARENTCATEGORY, IDCATEGORY, 1 AS LVL FROM TNODES
UNION ALL
SELECT pr.IDBRANCH, p.IDPARENTCATEGORY, p.IDCATEGORY, LVL+1
FROM BRANCH pr, TNODES p
WHERE p.IDCATEGORY = pr.IDPARENTCATEGORY
)
SELECT IDBRANCH, IDCATEGORY, IDPARENTCATEGORY, LVL
FROM BRANCH;
SELECT * FROM VNODES WHERE IDBRANCH = 122 ORDER BY LVL ASC;
http://sqlfiddle.com/#!11/42870/2
For Oracle, as requested in the comments, you can use the connect by operator to produce the hierarchy, and the level pseudocolumn to get the depth:
SELECT nodeid, parentid, LEVEL
FROM t
START WITH parentid IS NULL
CONNECT BY parentid = PRIOR nodeid;
I'm not very experienced with advance SQL queries, I'm familiar with basic statements and basic joins, currently trying to figure out how to write a query that seems to be out of my depth and I haven't been able to find a solution from google so far and I'm hoping somebody might be able to point me in the right direction.
The table I'm working with has an ID column, and a 'parent id' column.
I'm looking for all descendants of ID '1' - rows with a parent ID of '1', rows with a parent ID equal to any row's ID with a parent ID of '1' etc. Currently I've been doing this manually but there are hundreds of descendants so far and I feel like there's a way to put this into one query.
Any help would be appreciated, if this is unclear I can also try to clarify.
EDIT - I got it working with the following query:
with cteMappings as (
select map_id, parent_map_id, map_name
from admin_map
where map_id = '1'
union all
select a.map_id, a.parent_map_id, a.map_name
from admin_map a
inner join cteMappings m
on a.parent_map_id = m.map_id
)
select map_id, parent_map_id, map_name
from cteMappings
Sounds like it can be achieved by Common Table Expression:
DECLARE #temp TABLE (id INT IDENTITY(1, 1), parent_id INT);
INSERT #temp
SELECT NULL
UNION ALL
SELECT 1
UNION ALL
SELECT 2
UNION ALL
SELECT NULL
SELECT * FROM #temp
; WITH HierarchyTemp (id, parent_id, depth) AS (
SELECT id, parent_id, 0
FROM #temp
WHERE id = 1
UNION ALL
SELECT t.id, t.parent_id, ht.depth + 1
FROM #temp t
INNER JOIN HierarchyTemp ht ON ht.id = t.parent_id
)
SELECT *
FROM HierarchyTemp
So the above example is creating a table variable with 4 rows:
id parent_id
1 NULL
2 1
3 2
4 NULL
Result of descendent of id '1' (also including itself, but can be excluded with an additional WHERE clause):
id parent_id depth
1 NULL 0
2 1 1
3 2 2
My situation:
Table A
(
ID
Parent_Id
TimeStamp
)
The root has Parent_Id null and children has Id of its father.
I simple want to get all LAST children of every Table A.
Father and Children I don't want. (except last one).
Is it possible to build a SQL to get this?
PS: I'm on sql anywhere 11. Maybe an ansi sql can solve this, i'm not sure.
EDIT: (edited to give additional details)
I don't want the last children from an element.
Example:
Id 1
Parent NULL
Id 2
Parent 1
Id 3 (the last child)
Parent 1
Id 4
Parent NULL
Id 5 (the last child)
parent 4
I want to get:
Id 3
Id 5
Using stored function
create function LastChild(in parent integer)
returns integer
begin
declare res integer;
select top 1 id into res from TableA where parent_id = parent order by timeCol desc;
return res;
end
select
select Id, lastchild(id) from TAbleA where parent_id is null
I'll work on another solution without stored function.
EDIT: without stored function:
select Id, (select top 1 id from TableA childs where parent_id = TableA.id order by timeCol desc) from TableA where parent_id = 0
If by "last children" you mean items that themselves have no children (and often referred to as leaf-level items), something like this should do:
SELECT ID
from A
where ID not in (select Parent_Id from A)
The correlated subquery version is a bit tricker to understand, but would work faster on large tables:
SELECT ID
from A OuterReference
where not exists (select 1 from A where Parenti_ID = OuterReference.ID)
("OuterReference" is an alias for table A)
I use SQL Server, but this is pretty basic syntax and should work for you with minimal modification.
select * from a where id not in (select parent_id from table a)
In other words, select everything from table a where the ID of the item is not the parent ID of any other item. This will give you all the leaf nodes of the graph.
EDIT:
Your edit is a bit confusing, and ID's aren't typically used as ordering mechanisms, but regardless, the example you give can be accomplished by this query
SELECT MAX( id )
FROM a
WHERE id NOT IN
(SELECT parent_id
FROM a
WHERE parent_id IS NOT NULL
)
GROUP BY parent_id
I had to update the query a little to get only child categories, for Postgres 9.4
select count(id) from A as outer_ref where not exists(
select 1 from A where parent_id=outer_ref.id) and parent_id is not null;
I have a tree in my database that is stored using parent id links.
A sample of what I have for data in the table is:
id | name | parent id
---+-------------+-----------
0 | root | NULL
1 | Node 1 | 0
2 | Node 2 | 0
3 | Node 1.1 | 1
4 | Node 1.1.1 | 3
5 | Node 1.1.2 | 3
Now I would like to get a list of all the direct descendants of a given node but if none exist I would like to have it just return the node itself.
I want the return for the query for children of id = 3 to be:
children
--------
4
5
Then the query for the children of id = 4 to be:
children
--------
4
I can change the way I am storing the tree to a nested set but I don't see how that would make the query I want possible.
In new PostgreSQL 8.4 you can do it with a CTE:
WITH RECURSIVE q AS
(
SELECT h, 1 AS level, ARRAY[id] AS breadcrumb
FROM t_hierarchy h
WHERE parent = 0
UNION ALL
SELECT hi, q.level + 1 AS level, breadcrumb || id
FROM q
JOIN t_hierarchy hi
ON hi.parent = (q.h).id
)
SELECT REPEAT(' ', level) || (q.h).id,
(q.h).parent,
(q.h).value,
level,
breadcrumb::VARCHAR AS path
FROM q
ORDER BY
breadcrumb
See this article in my blog for details:
PostgreSQL 8.4: preserving order for hierarchical query
In 8.3 or earlier, you'll have to write a function:
CREATE TYPE tp_hierarchy AS (node t_hierarchy, level INT);
CREATE OR REPLACE FUNCTION fn_hierarchy_connect_by(INT, INT)
RETURNS SETOF tp_hierarchy
AS
$$
SELECT CASE
WHEN node = 1 THEN
(t_hierarchy, $2)::tp_hierarchy
ELSE
fn_hierarchy_connect_by((q.t_hierarchy).id, $2 + 1)
END
FROM (
SELECT t_hierarchy, node
FROM (
SELECT 1 AS node
UNION ALL
SELECT 2
) nodes,
t_hierarchy
WHERE parent = $1
ORDER BY
id, node
) q;
$$
LANGUAGE 'sql';
and select from this function:
SELECT *
FROM fn_hierarchy_connect_by(4, 1)
The first parameter is the root id, the second should be 1.
See this article in my blog for more detail:
Hierarchical queries in PostgreSQL
Update:
To show only the first level children, or the node itself if the children do not exist, issue this query:
SELECT *
FROM t_hierarchy
WHERE parent = #start
UNION ALL
SELECT *
FROM t_hierarchy
WHERE id = #start
AND NOT EXISTS
(
SELECT NULL
FROM t_hierarchy
WHERE parent = #start
)
This is more efficient than a JOIN, since the second query will take but two index scans at most: the first one to make sure to find out if a child exists, the second one to select the parent row if no children exist.
Found a query that works the way I wanted.
SELECT * FROM
( SELECT id FROM t_tree WHERE name = '' ) AS i,
t_tree g
WHERE
( ( i.id = g.id ) AND
NOT EXISTS ( SELECT * FROM t_tree WHERE parentid = i.id ) ) OR
( ( i.id = g.parentid ) AND
EXISTS ( SELECT * FROM t_tree WHERE parentid = i.id ) )