Comment by ars

It's not silent:

    mysql> insert into demo values ('y', 'y');
    Query OK, 1 row affected, 1 warning (0.01 sec)

    mysql> show warnings;
    +---------+------+------------------------------------------------------+
    | Level   | Code | Message                                              |
    +---------+------+------------------------------------------------------+
    | Warning | 1366 | Incorrect integer value: 'y' for column 'n' at row 1 |
    +---------+------+------------------------------------------------------+

If you want this type of warning to be treated as an error then adjust the setting:

    mysql> SET sql_mode = 'TRADITIONAL';
    mysql> insert into demo values ('y', 'y');
    ERROR 1366 (HY000): Incorrect integer value: 'y' for column 'n' at row 1