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CREATE TABLE table1 (
`id` INTEGER,
`deadline_date` DATE,
`reminder1` DATE,
`reminder2` DATE,
`reminder3` DATE
);
INSERT INTO table1
(`id`, `deadline_date`, `reminder1`, `reminder2`, `reminder3`)
VALUES
('1', '2021-04-26', NULL, NULL, NULL);
UPDATE table1 t1
SET t1.`reminder1` = t1.`deadline_date` - INTERVAL 1 DAY - INTERVAL 2 MONTH,
t1.`reminder2` = t1.`deadline_date` - INTERVAL 1 DAY - INTERVAL 1 MONTH,
t1.`reminder3` = t1.`deadline_date` - INTERVAL 1 DAY;
SELECT * FROM table1
| id | deadline_date | reminder1 | reminder2 | reminder3 |
|---|---|---|---|---|
| 1 | 2021-04-26 | 2021-02-25 | 2021-03-25 | 2021-04-25 |