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CREATE TABLE table_name
(`a` int)
;
INSERT INTO table_name
(`a`)
VALUES
(1),
(4),
(8),
(9)
;
select * from
(select lead(a) over(order by a) - a as a
from table_name) t
where a is not null;
| a |
|---|
| 3 |
| 4 |
| 1 |