MySQL 8.0

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CREATE TABLE t1 (id INT PRIMARY KEY, val INT);
CREATE TABLE t2 (id INT PRIMARY KEY, val INT);
INSERT INTO t1 VALUES (1,1), (2,2);
INSERT INTO t2 VALUES (1,1), (3,3);
SELECT * FROM t1;
SELECT * FROM t2;

Records: 2  Duplicates: 0  Warnings: 0

Records: 2  Duplicates: 0  Warnings: 0

id
val

1
1

2
2

id
val

1
1

3
3

CREATE TRIGGER tr_au_t1
AFTER UPDATE ON t1
FOR EACH ROW
BEGIN
    IF @check_for_cycle IS NULL THEN
        SET @check_for_cycle := 1;
        UPDATE t2 SET val = NEW.val + 10 WHERE id = NEW.id;
        SET @check_for_cycle := NULL;
    END IF;
END
CREATE TRIGGER tr_au_t2
AFTER UPDATE ON t2
FOR EACH ROW
BEGIN
    IF @check_for_cycle IS NULL THEN
        SET @check_for_cycle := 1;
        UPDATE t1 SET val = NEW.val + 100 WHERE id = NEW.id;
        SET @check_for_cycle := NULL;
    END IF;
END
UPDATE t1 SET val = val + 1;
SELECT * FROM t1;
SELECT * FROM t2;

Rows matched: 2  Changed: 2  Warnings: 0

id
val

1
2

2
3

id
val

1
12

3
3

UPDATE t2 SET val = val + 2;
SELECT * FROM t1;
SELECT * FROM t2;

Rows matched: 2  Changed: 2  Warnings: 0

id
val

1
114

2
3

id
val

1
14

3
5