drop table if exists t1;

create table t1 (pk int, c int);

insert into t1 values (1,1),(2,1),(3,1),(4,1),(5,2);

set sql_mode='ERROR_FOR_DIVISION_BY_ZERO';

select pk, c, c/count(*) over (partition by c order by pk

rows between 1 preceding and 2 following) as CNT

from t1;

show warnings;

drop table t1;

MariaDB [test]> select pk, c, c/count(*) over (partition by c order by pk

    -> rows between 1 preceding and 2 following) as CNT

    -> from t1;

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

| pk   | c    | CNT    |

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

|    1 |    1 | 0.3333 |

|    2 |    1 | 0.2500 |

|    3 |    1 | 0.3333 |

|    4 |    1 | 0.5000 |

|    5 |    2 | 2.0000 |

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

5 rows in set, 5 warnings (0.00 sec)

MariaDB [test]> show warnings;

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

| Level   | Code | Message       |

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

| Warning | 1365 | Division by 0 |

| Warning | 1365 | Division by 0 |

| Warning | 1365 | Division by 0 |

| Warning | 1365 | Division by 0 |

| Warning | 1365 | Division by 0 |

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

5 rows in set (0.00 sec)