def remove_schema(self, database, schema):
        """Remove a schema from the set of known schemas (case-insensitive)

        If the schema does not exist, it will be ignored - it could just be a
        temporary table.

        :param str database: The database name to remove.
        :param str schema: The schema name to remove.
        """
        self.schemas.discard((_lower(database), _lower(schema)))