SQLite 3.27

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CREATE TABLE tablename (`id` INTEGER, `val_1` INTEGER, `val_2` INTEGER);
INSERT INTO tablename (`id`, `val_1`, `val_2`) VALUES
  ('1', '55', '300'),
  ('2', '90', '600'),
  ('3', '80', '200');
SELECT *, 
       val_2 - LEAD(val_1, 1, 0) OVER (ORDER BY id) AS difference
FROM tablename;


id
val_1
val_2
difference


1
55
300
210

2
90
600
520

3
80
200
200


SELECT *, 
       LAG(val_2, 1, 0) OVER (ORDER BY id) - val_1 AS difference
FROM tablename;


id
val_1
val_2
difference


1
55
300
-55

2
90
600
210

3
80
200
520