def get_pre_alter_table_index_foreign_key_sql(self, diff):
        """
        :param diff: The table diff
        :type diff: orator.dbal.table_diff.TableDiff

        :rtype: list
        """
        if not isinstance(diff.from_table, Table):
            raise DBALException(
                "Sqlite platform requires for alter table the table"
                "diff with reference to original table schema"
            )

        sql = []
        for index in diff.from_table.get_indexes().values():
            if not index.is_primary():
                sql.append(self.get_drop_index_sql(index, diff.name))

        return sql
:param diff: The table diff
        :type diff: orator.dbal.table_diff.TableDiff

        :rtype: list