MariaDB [test]> CREATE TABLE tb1 (a int, b int, PRIMARY KEY (a));

Query OK, 0 rows affected (0.055 sec)

MariaDB [test]> insert into tb1 values (1,5),(2,5),(3,5);

Query OK, 3 rows affected (0.009 sec)

Records: 3  Duplicates: 0  Warnings: 0

MariaDB [test]> insert into tb1 (a,b)

    -> select a,6 from tb1 t1

    -> on duplicate key update b=(select t2.d from ((select 1 c,1 d) union (values (2,20),(3,33))) t2 where t2.c=t1.a);

Query OK, 6 rows affected (0.010 sec)

Records: 3  Duplicates: 3  Warnings: 0

MariaDB [test]> select * from tb1;

+---+------+

| a | b    |

+---+------+

| 1 |   33 |

| 2 |   33 |

| 3 |   33 |

+---+------+

3 rows in set (0.002 sec)

MariaDB [test]> select version();

+----------------------+

| version()            |

+----------------------+

| 10.9.2-MariaDB-debug |

+----------------------+

1 row in set (0.001 sec)