Add a schema to the set of known schemas (case-insensitive)

        :param str database: The database name to add.
        :param str schema: The schema name to add.

def add_schema(self, database, schema):
        """Add a schema to the set of known schemas (case-insensitive)

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