How do I sort a linked list in sql?

Question

I have implemented a linked list as a self-referencing database table:

CREATE TABLE LinkedList(
    Id bigint NOT NULL,
    ParentId bigint NULL,
    SomeDat         


        

Answer 1

In Oracle:

SELECT Id, ParentId, SomeData
FROM (
  SELECT ll.*, level AS lvl
  FROM LinkedList ll
  START WITH
    ParentID IS NULL
  CONNECT BY
    ParentId = PRIOR Id
)
ORDER BY
  lvl

P. S. It's a bad practice to use NULL as ParentID, as it is not searchable by indices. Insert a surrogate root with id of 0 or -1 instead, and use START WITH ParentID = 0.