MySQL 8.0

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create table t as
    select N'The hills have eyes. 隔山有眼' as str
select replace(convert(t.str using ascii), '?', '')
from t

replace(convert(t.str using ascii), '?', '')

The hills have eyes.

select regexp_replace(t.str, '[^a-zA-Z0-9.? ]', '')
from t

regexp_replace(t.str, '[^a-zA-Z0-9.? ]', '')

The hills have eyes.