How to use min() together with other column in SQL - sql

Question

I am building an application consisting of an SQL backend and several microservices that communicate with this backend. I am trying to get as little data as possible from the database over the wire so I am trying to fetch the exact records so I don't have to start looping in the application logic.
So this is the source table :
OrderID
Topic
hierarchyLevel
Responsible Person
Status
1234
A
0
Jason
Open
1234
A
0
Carol
Open
1234
A
1
Jeff
Open
1234
A
2
Alina
Open
1234
A
3
Eileen
Open
1234
B
0
John
Closed
1234
B
1
Danny
Open
1234
B
1
Celine
Open
1234
B
2
Corry
Open
1234
B
3
Logan
Open
1234
C
0
Jason
Closed
1234
C
1
Annisa
Open
1234
C
2
Cedric
Open
1234
D
0
Peter
Closed
1234
D
1
Joanna
Closed
1234
D
2
Freeke
Open
1234
E
0
Carol
Closed
1234
E
1
Cynthia
Closed
1234
E
2
Deidra
Open
Based on the "orderID" as input parameter for the query , I should get the for every topic the next persons in line , so with the lowest HierarchyLevel number for that topic, that has status "Open". So every topic can return multiple times as long as the returned records have the lowest possible value in "HierarchyLevel" and the status is "Open".
So I would expect this as output for the stored procedure :
OrderID
Topic
hierarchyLevel
Responsible Person
Status
1234
A
0
Jason
Open
1234
A
0
Carol
Open
1234
B
1
Danny
Open
1234
B
1
Celine
Open
1234
C
1
Annisa
Open
1234
D
2
Freeke
Open
1234
E
2
Deidra
Open
I tried to work with min() but with no luck:
Some things I tried :
select * from mytable as a
inner join (
select Topic, min(HierarchyLevel) as min_value
from mytable
group by Topic
) t on t.Topic = a.Topic and a.HierarchyLevel = min_value and a.OrderID = #OrderID and Status = 'Open'
select * from mytable as a
inner join (
select Topic, Status ,min(HierarchyLevel) as min_value
from mytable
group by Topic , Status HAVING Status = 'Open'
) t on t.Topic = a.Topic and a.HierarchyLevel = min_value and a.OrderID = #OrderID and a.Status = 'Open'
None with the desired result. Could anyone guide me in the right direction?
Thank you very much.

Answer 1

Lookup RANK() OVER (...). I guess something like:
SELECT OrderID, Topic, hierarchyLevel, Responsible_Person, Status
FROM (
SELECT OrderID, Topic, hierarchyLevel, Responsible_Person, Status
, RANK() OVER (PARTITION BY OrderID, Topic
ORDER BY hierarchyLevel) AS rnk
FROM t
WHERE Status = 'Open'
) AS T
WHERE rnk = 1;

Answer 2

One straight-forward solution is to use a correlated aggregate using exists:
select *
from t
where exists (
select * from t t2
where t2.OrderId = t.OrderId
and t2.Topic = t.Topic
and t2.Status = 'Open'
group by t2.OrdeRId, t2.Topic
having Min(t2.hierarchyLevel) = t.hierarchyLevel
);
Demo DB<>Fiddle
Result:

Answer 3

One way is to check if all the records with open status intersect with said records also having the lowest heirarchy_level per order_id and topic
select order_id, topic, heirarchy_level, responsible_person, status
from t
where status='Open'
intersect
select order_id, topic, min(heirarchy_level) over (partition by order_id, topic), responsible_person, status
from t
where status='Open'