Avoid NULL values in result set of sub-query

    private static void cleanUpMessagePartsTable(SQLiteDatabase db) {

        db.execSQL("DELETE FROM message_parts WHERE root NOT IN " +

                "(SELECT message_part_id FROM messages WHERE deleted = 0)");

                "(SELECT message_part_id FROM messages WHERE deleted = 0 AND message_part_id IS NOT NULL)");

    }

    static void createDeleteMessageTrigger(SQLiteDatabase db) {