def unsetrange(self, keys=None, prefix=""):
        """
        Remove a range of keys starting with a common prefix, from the database
        entirely.

        :param list keys: List of keys to remove.
        :param str prefix: Optional prefix to apply to all keys in ``keys``
            before removing.
        """
        if keys is not None:
            keys = ['%s%s' % (prefix, key) for key in keys]
            self.cursor.execute('delete from kv where key in (%s)' % ','.join(['?'] * len(keys)), keys)
            if self.revision and self.cursor.rowcount:
                self.cursor.execute(
                    'insert into kv_revisions values %s' % ','.join(['(?, ?, ?)'] * len(keys)),
                    list(itertools.chain.from_iterable((key, self.revision, json.dumps('DELETED')) for key in keys)))
        else:
            self.cursor.execute('delete from kv where key like ?',
                                ['%s%%' % prefix])
            if self.revision and self.cursor.rowcount:
                self.cursor.execute(
                    'insert into kv_revisions values (?, ?, ?)',
                    ['%s%%' % prefix, self.revision, json.dumps('DELETED')])
Remove a range of keys starting with a common prefix, from the database
        entirely.

        :param list keys: List of keys to remove.
        :param str prefix: Optional prefix to apply to all keys in ``keys``
            before removing.