MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
select version();


version()


8.0.30


CREATE TABLE mytable (
  Number INTEGER,
  Parent INTEGER);
INSERT INTO mytable VALUES
  (1,NULL),
  (2,1),
  (3,2);

Records: 3  Duplicates: 0  Warnings: 0


WITH recursive cte AS (
  SELECT 
     Number, 
     Parent 
  FROM mytable 
  WHERE mytable.Number=3
  
  UNION ALL
  
  SELECT 
     mytable.Number, 
     mytable.Parent 
  FROM cte
  INNER JOIN mytable ON mytable.Number = cte.Parent
)
SELECT * FROM cte;



Number
Parent


3
2

2
1

1
null


WITH recursive cte AS (
  SELECT 
     Number, 
     Parent 
  FROM mytable 
  WHERE mytable.Number=2
  
  UNION ALL
  
  SELECT 
     mytable.Number, 
     mytable.Parent 
  FROM cte
  INNER JOIN mytable ON mytable.Number = cte.Parent
)
SELECT * FROM cte;



Number
Parent


2
1

1
null


WITH recursive cte AS (
  SELECT 
     Number, 
     Parent 
  FROM mytable 
  WHERE mytable.Number=1
  
  UNION ALL
  
  SELECT 
     mytable.Number, 
     mytable.Parent 
  FROM cte
  INNER JOIN mytable ON mytable.Number = cte.Parent
)
SELECT * FROM cte;



Number
Parent


1
null