What are the situations where you wouldn't want to check cursor.fetchone() for None? I guess when you are checking cursor.rowcount beforehand, but in general I feel that not checking the result of fetchone() for None is a mistake that the type checker should catch.

Here's my actual code where I don't want to check for it:

        self._cursor.execute("select connection_id() as id")
        self._connection_id = self._cursor.fetchone()["id"]  # type: ignore

As far as I can tell, fetchone() will always succeed in this case, since the select always outputs a row. But I think this is somewhat rare and it might be better to just return Optional[Dict[str, Any]] (but still, not a Union containing tuples too).

You are right, I actually have similar code, where I know the exact number of rows and columns returned (for example SELECT COUNT(*) FROM foo). But since this is a fairly sensitive I do prefer the Optional (or | None), despite the slight inconvenience, even though this is a violation of our "prefer false negatives over false positives" principle.

Haha, I just opened my IDE and it automatically opened to this piece of code:

        query = (
            "SELECT "
            "COUNT(*), "
            "SUM(CASE WHEN benutzer.kuerzel LIKE 'B%' THEN 0 ELSE 1 END) "
            "FROM patienten LEFT OUTER JOIN benutzer "
            "ON patienten.behandlerid = benutzer.solid "
            "WHERE passiv = 0 AND behandelt_seit >= ? AND behandelt_seit < ?"
        )
        rows = store.execute_sql(query, [dt1, dt2])
        assert rows is not None
        assert len(rows) == 1
        return rows[0][0], rows[0][1] or 0

(Although it's using SQLalchemy, not pymysql directly.)