I want to know the algorithm behind child nested records are displayed within parent nested records for example
Comment 1 (parent record)
reply 1 (child record)
reply 2 (child record)
reply 3 (child record)
view all
Comment 2 (parent record)
reply 1 (child record)
reply 2 (child record)
reply 3 (child record)
view all
how is a query written to get the above results?
You can use a Recursive Common Table Expression like the one below
;WITH comments AS
(
SELECT 1 as ID,'Comment 1' detail,NULL AS ParentID
UNION ALL SELECT 2 as ID,'Comment 2',NULL AS ParentID
UNION ALL SELECT 3 as ID,'Reply 1',1 AS ParentID
UNION ALL SELECT 4 as ID,'Reply 2',3 AS ParentID
UNION ALL SELECT 5 as ID,'Reply 3',4 AS ParentID
UNION ALL SELECT 6 as ID,'Reply 4',2 AS ParentID
UNION ALL SELECT 7 as ID,'Reply 5',6 AS ParentID
),comment_hierarchy AS
(
SELECT ID,detail,ID AS prid,0 AS orderid
FROM comments
WHERE ParentID IS NULL
UNION ALL
SELECT c.ID,c.detail ,ch.prid as prid,ch.orderid + 1
FROM comments c
INNER JOIN comment_hierarchy ch
ON c.ParentID = ch.ID
)
SELECT ID,Detail
FROM comment_hierarchy
ORDER BY prid,orderid asc
For more info refer
https://technet.microsoft.com/en-us/library/ms186243%28v=sql.105%29.aspx
CTE to get all children (descendants) of a parent
Related
I have a table with parent child relationships and I want to, for each child, display the upper most parent. The order of the real table won't be ordered so consecutively so any kind of sorting isn't desirable. I also want to avoid doing manual joins for the max number of hierarchy levels.
Table:
Parent Child
1 2
2 3
3 4
5 6
6 7
So for Child 4 has Parent 3, who has Parent 2, who has Parent 1.
4, 3, 2 should all have Parent 4 in the output.
Desired Output:
Parent Child
1 2
1 3
1 4
5 6
5 7
;with SelectedToTopCTE as
( select ParentID, ChildID as Child, 1 as level
from Table
union all
select d.ParentID, s.ChildID, d.level + 1
from SelectedToTopCTE as d
join Table s
on d.Child = s.ParentID
)
select * INTO #SelectedToTop
from SelectedToTopCTE;
SELECT Child, MAX(level) as MaxLevel INTO #UpperMostSPLT
FROM #SelectedToTop
group by Child;
SELECT A.*
FROM #SelectedToTop A
INNER JOIN
#UpperMostSPLT B
ON A.Child = B.Child AND A.level = B.MaxLevel
ORDER BY ParentID;
A recursive Common Table Expression (CTE) makes quick work of walking through parent/child hierarchies. This example starts with the top level parents, i.e. the rows that have no parents above them. It then adds children one level at a time while keeping track of the topmost parent.
-- Sample data.
declare #Samples as Table ( Parent Int, Child Int );
insert into #Samples ( Parent, Child ) values
( 1, 2 ), ( 2, 3 ), ( 3, 4 ), ( 5, 6 ), ( 6, 7 );
select * from #Samples;
-- Run the tree.
with Tree as (
-- Start with the top level parents.
select Parent as TopLevelParent, Child
from #Samples as S
-- Where the row has no parent above it.
where not exists ( select 42 from #Samples as SS where S.Parent = SS.Child )
union all
-- Add the children one level at a time.
select T.TopLevelParent, S.Child
from Tree as T inner join
#Samples as S on S.Parent = T.Child )
-- Display the sorted results.
select TopLevelParent, Child
from Tree
order by TopLevelParent, Child;
Scenario:
I have data in the following hierarchy format in my table:
PERSON_ID Name PARENT_ID
1 Azeem 1
2 Farooq 2
3 Ahsan 3
4 Waqas 1
5 Adnan 1
6 Talha 2
7 Sami 2
8 Arshad 2
9 Hassan 8
E.g
Hassan is child of parent_id 8 which is (Arshad)
and Arshad is child of parent_id 2 which is (Farooq)
What I want:
First of all, I want to find all parent of parent of specific parent_id.
For Example: If I want to find the parent of Hassan then I also get the Parent of Hassan and also get its parent (Hassan -> Arshad -> Farooq)
Second, I want to find all child of Farooq like (Farooq -> Arshad -> Hassan)
Third, If Azeem is also have same parent like (Azeem -> Azeem) then show me this record.
What I've tried yet:
DECLARE #id INT
SET #id = 9
;WITH T AS (
SELECT p.PERSON_ID,p.Name, p.PARENT_ID
FROM hierarchy p
WHERE p.PERSON_ID = #id AND p.PERSON_ID != p.PARENT_ID
UNION ALL
SELECT c.PERSON_ID,c.Name, c.PARENT_ID
FROM hierarchy c
JOIN T h ON h.PARENT_ID = c.PERSON_ID)
SELECT h.PERSON_ID,h.Name FROM T h
and Its shows me below error:
The statement terminated. The maximum recursion 100 has been exhausted before statement completion.
If I understand your question correctly that you don't want to insert null values in Parent_ID column then you should replace NULL with 0 and your updated code will be like:
;WITH DATA AS (
SELECT p.PERSON_ID,p.Name, p.PARENT_ID
FROM hierarchy p
WHERE p.PERSON_ID = 9
UNION ALL
SELECT c.PERSON_ID,c.Name, c.PARENT_ID
FROM hierarchy c
JOIN DATA h
ON c.PERSON_ID = h.PARENT_ID
)
select * from DATA;
You have an infinite loop in your data: Azeem is his own parent. You need to either make his value NULL or change your condition to WHERE p.parent_id = #id AND p.parent_id != p.child_id.
Also, I feel you have your columns named the wrong way around - the primary-key should be named person_id instead of parent_id and your column named child_id actually points to that person's parent, so it should be named parent_id instead.
Well I found a way for my above case which is:
If I have below table structure:
PERSON_ID Name PARENT_ID
1 Azeem NULL
2 Farooq NULL
3 Ahsan NULL
4 Waqas 1
5 Adnan 1
6 Talha 2
7 Sami 2
8 Arshad 2
9 Hassan 8
Then I tried below query which working fine in case when Parent_ID have NULL values means there is no more parent of that record.
DECLARE #id INT
SET #id = 2
Declare #Table table(
PERSON_ID bigint,
Name varchar(50),
PARENT_ID bigint
);
;WITH T AS (
SELECT p.PERSON_ID,p.Name, p.PARENT_ID
FROM hierarchy p
WHERE p.PERSON_ID = #id AND p.PERSON_ID != p.PARENT_ID
UNION ALL
SELECT c.PERSON_ID,c.Name, c.PARENT_ID
FROM hierarchy c
JOIN T h ON h.PARENT_ID = c.PERSON_ID)
insert into #table
select * from T;
IF exists(select * from #table)
BEGIN
select PERSON_ID,Name from #table
End
Else
Begin
select PERSON_ID,Name from Hierarchy
where PERSON_ID = #id
end
Above query show me the desire output when I set the parameter value #id = 1
Above query show me the desire output when I set the parameter value #id = 9
Issue:
I don't want to insert null values in Parent_ID like if there is no more Parent of that Person then I insert same Person_ID in Parent_ID column.
If I replace null values with there person_id then I got below error.
The statement terminated. The maximum recursion 100 has been exhausted before statement completion.
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
I have a table where I have menus listed where I can insert and delete.
Structure goes like:-
ID Name ParentId
1 1. Home 0
2 2. Products 0
3 a. SubProduct1 2
4 b. SubProduct2 2
5 i. Subsub 4
6 ii. ...... 4
7 3. About 0
Top-level menu ParentId is always 0 as displayed in 1, 2 and 7.
Child level items would have ParentId of their parent for ex. Subproduct has 2 as its parentId.
When I delete menu item that time all level child item should be delete irrespective of there levels using SQL query.
There can be any number of levels
The levels can go upto subsubsubsub...... any number.
How about this query:
DECLARE #DelID INT
SET #DelID=1
;WITH T(xParent, xChild)AS
(
SELECT ParentID, ChildId FROM Table WHERE ParentID=#DelID
UNION ALL
SELECT ParentID, ChildId FROM TABLE INNER JOIN T ON ParentID=xChild
)
DELETE FROM TABLE WHERE ParentID IN (SELECT xParent FROM T)
You can use a common table expression to get all the heirarchy items from the item you want to delete to the end of the tree hten
;WITH ParentChildsTree
AS
(
SELECT ID, Name, ParentId
FROM MenuItems
WHERE Id = #itemToDelete
UNION ALL
SELECT ID, Name, ParentId
FROM ParentChildsTree c
INNER JOIN MenuItems t ON c.ParentId = t.Id
)
DELETE FROM MenuItems
WHERE ID IN (SELECT ID FROM ParentChildsTree);
Here is a Demo.
For example if you pass a parameter #itemToDelete = 4 to the query the the items with ids 2 and 4 will be deleted.
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