create database d1;

use d1;

create table t1 (id int ,PRIMARY KEY (id) );

create table t2 (id int ,PRIMARY KEY (id) );

insert into t1 (id) values (1),(2),(3),(4);

insert into t2 (id) values (1),(2),(3),(4);

set autocommit = 0;

explain update t2 set id = (select id from t1);

set autocommit = 0;

explain update t2 set id = (select id from t1);

MariaDB [d1]> select * from t1;

+----+

| id |

+----+

|  1 |

|  2 |

|  3 |

|  4 |

+----+

4 rows in set (0.000 sec)

MariaDB [d1]> commit;

Query OK, 0 rows affected (0.000 sec)

MariaDB [d1]> select * from t1;

+----+

| id |

+----+

|  1 |

|  2 |

|  3 |

|  4 |

|  5 |

+----+

5 rows in set (0.000 sec)