SQL Order by parent and child - mysql

Question

Basically I need help in my query here. I want to be in right order which is child must be under parents name and in A-Z order. But if I add a subChild under child (Split 1) seem the order is wrong. It should be under Room Rose.
p/s : A subChild also can create another subChild
HERE I PROVIDE A DEMO
Appreciate your help me get this ordered correctly?
SELECT A.venueID
, B.mainVenueID
, A.venueName
FROM tblAdmVenue A
LEFT
JOIN tblAdmVenueLink B
ON A.venueID = B.subVenueID
ORDER
BY COALESCE(B.mainVenueID, A.venueID)
, B.mainVenueID IS NOT NULL
, A.venueID
I want it return an order something like this.
venueName
--------------
Banquet
Big Room
-Room Daisy
-Room Rose
-Split 1
Hall
-Meeting Room WP
Seem this recursive approach also in not working
WITH venue_ctg AS (
SELECT A.venueID, A.venueName, B.mainVenueID
FROM tblAdmVenue A LEFT JOIN tblAdmVenueLink B
ON A.venueID = B.subVenueID
WHERE B.mainVenueID IS NULL
UNION ALL
SELECT A.venueID, A.venueName, B.mainVenueID
FROM tblAdmVenue A LEFT JOIN tblAdmVenueLink B
ON A.venueID = B.subVenueID
WHERE B.mainVenueID IS NOT NULL
)
SELECT *
FROM venue_ctg ORDER BY venueName
output given

Answer 1

For your data you can use this:
To display this correctly, you can use a SEPARATPR like comma, and split the returned data, and check the hirarchy
-- schema
CREATE TABLE tblAdmVenue (
venueID VARCHAR(225) NOT NULL,
venueName VARCHAR(225) NOT NULL,
PRIMARY KEY(venueID)
);
CREATE TABLE tblAdmVenueLink (
venueLinkID VARCHAR(225) NOT NULL,
mainVenueID VARCHAR(225) NOT NULL,
subVenueID VARCHAR(225) NOT NULL,
PRIMARY KEY(venueLinkID)
-- FOREIGN KEY (DepartmentId) REFERENCES Departments(Id)
);
-- data
INSERT INTO tblAdmVenue (venueID, venueName)
VALUES ('LA43', 'Big Room'), ('LA44', 'Hall'),
('LA45', 'Room Daisy'), ('LA46', 'Room Rose'),
('LA47', 'Banquet'), ('LA48', 'Split 1'),
('LA49', 'Meeting Room WP');
INSERT INTO tblAdmVenueLink (venueLinkID, mainVenueID, subVenueID)
VALUES ('1', 'LA43', 'LA45'), ('2', 'LA43', 'LA46'),
('3', 'LA46', 'LA48'), ('4', 'LA44', 'LA49');
✓
✓
✓
✓
with recursive cte (subVenueID, mainVenueID,level) as (
select subVenueID,
mainVenueID, 1 as level
from tblAdmVenueLink
union
select p.subVenueID,
cte.mainVenueID,
cte.level+1
from tblAdmVenueLink p
inner join cte
on p.mainVenueID = cte.subVenueID
)
select
CONCAT(GROUP_CONCAT(b.venueName ORDER BY level DESC SEPARATOR '-->') ,'-->',a.venueName)
from cte c
LEFT JOIN tblAdmVenue a ON a.venueID = c.subVenueID
LEFT JOIN tblAdmVenue b ON b.venueID = c.mainVenueID
GROUP BY subVenueID;
| CONCAT(GROUP_CONCAT(b.venueName ORDER BY level DESC SEPARATOR '-->') ,'-->',a.venueName) |
| :----------------------------------------------------------------------------------------- |
| Big Room-->Room Daisy |
| Big Room-->Room Rose |
| Big Room-->Room Rose-->Split 1 |
| Hall-->Meeting Room WP |
db<>fiddle here

Answer 2

You want your data ordered in alphabetical order and depth first.
A common solution for this is to traverse the structure from the top element, concatenating the path to each item as you go. You can then directly use the path for ordering.
Here is how to do it in MySQL 8.0 with a recursive query
with recursive cte(venueID, venueName, mainVenueID, path, depth) as (
select v.venueID, v.venueName, cast(null as char(100)), venueName, 0
from tblAdmVenue v
where not exists (select 1 from tblAdmVenueLink l where l.subVenueID = v.venueID)
union all
select v.venueID, v.venueName, c.venueID, concat(c.path, '/', v.venueName), c.depth + 1
from cte c
inner join tblAdmVenueLink l on l.mainVenueID = c.venueID
inner join tblAdmVenue v on v.venueID = l.subVenueID
)
select * from cte order by path
The anchor of the recursive query selects top nodes (ie rows whose ids do not exist in column subVenueID of the link table). Then, the recursive part follows the relations.
As a bonus, I added a level column that represents the depth of each node, starting at 0 for top nodes.
Demo on DB Fiddle:
venueID | venueName | mainVenueID | path | depth
:------ | :-------------- | :---------- | :------------------------- | ----:
LA47 | Banquet | null | Banquet | 0
LA43 | Big Room | null | Big Room | 0
LA45 | Room Daisy | LA43 | Big Room/Room Daisy | 1
LA46 | Room Rose | LA43 | Big Room/Room Rose | 1
LA48 | Split 1 | LA46 | Big Room/Room Rose/Split 1 | 2
LA44 | Hall | null | Hall | 0
LA49 | Meeting Room WP | LA44 | Hall/Meeting Room WP | 1

Answer 3

Use only one table, not two. The first table has all the info needed.
Then start the CTE with the rows WHERE mainVenueID IS NULL, no JOIN needed.
This may be a good tutorial: https://stackoverflow.com/a/18660789/1766831
Its 'forest' is close to what you want.

Answer 4

I suppose you have:
table tblAdmVenue A is the venue list; and
table tblAdmVenueLink B is the tree relation table for parent-child
For your question on how to get a correct sorting order, I think one of the trick is to concatenate the parent venue names.
with q0(venueID, venueName, mainVenueID, venuePath) as (
select
A.venueID,
A.venueName,
null,
A.venueName
from tblAdmVenue A
left join tblAdmVenue B on A.venueID = B.subVenueID
where B.mainVenueID is null
union all
select
A.venueID,
A.venueName,
q0.venueID,
q0.venuePath + char(9) + A.venueName
from q0
inner join tblAdmVenue B on q0.venueID = B.mainVenueID
inner join tblAdmVenue A on A.venueID = B.subVenueID
)
select venueID, venueName, mainVenueID
from q0
order by venuePath