MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE t (`name` VARCHAR(1) PRIMARY KEY, `value` INTEGER, `lastupdate` DATE);

INSERT INTO t (`name`, `value`, `lastupdate`) VALUES
  ('a', '10', '2021-01-01'),
  ('b', '20', '2021-02-01'),
  ('c', '30', '2021-03-01');

Records: 3  Duplicates: 0  Warnings: 0


INSERT INTO t (name, value, lastupdate) VALUES
  ('a', 20, '2021-01-01'),
  ('b', 40, '2021-01-01'),
  ('c', 60, '2021-04-01') AS new
ON DUPLICATE KEY UPDATE
t.value = CASE WHEN new.lastupdate >= t.lastupdate THEN new.value ELSE t.value END;

Records: 3  Duplicates: 2  Warnings: 0


SELECT * FROM t;


name
value
lastupdate


a
20
2021-01-01

b
20
2021-02-01

c
60
2021-03-01