Update Null value - sql

Question

This question reflects my issue. How to do this in SQLite?
I've tried UPDATE with self-joins, isolating the self join in sub-query, triggers, and something similar to this. Here is an example:
UPDATE stage
SET title =
(
SELECT
prior.title
FROM
stage prior,
stage now
WHERE
prior.rownum+1 = now.rownum
)
WHERE
title is null

Answer 1

Every table in SQLite has got a pseudo-column called rowid (which can be accessible under several different names: rowid, oid, _rowid_, unless those names are assigned to other, real, columns). The rowid column is essentially a unique row identifier and you can use it as a sort criterion and/or in conditions.
The following query demonstrates how your problem can be solved with the help of rowid:
UPDATE stage
SET title = (
SELECT title
FROM stage AS prev
WHERE title IS NOT NULL AND prev.rowid < stage.rowid
ORDER BY prev.rowid DESC
LIMIT 1
)
WHERE title IS NULL
Here's a demo on SQL Fiddle.
You can read more about rowid in this SQLite manual.

Answer 2

I presented a solution for the problem you referred (I successfully tested on SQL2008, SQLite3 and Oracle11g). I copied that solution below:
CREATE TABLE test(mysequence INT, mynumber INT);
INSERT INTO test VALUES(1, 3);
INSERT INTO test VALUES(2, NULL);
INSERT INTO test VALUES(3, 5);
INSERT INTO test VALUES(4, NULL);
INSERT INTO test VALUES(5, NULL);
INSERT INTO test VALUES(6, 2);
SELECT t1.mysequence, t1.mynumber AS ORIGINAL
, (
SELECT t2.mynumber
FROM test t2
WHERE t2.mysequence = (
SELECT MAX(t3.mysequence)
FROM test t3
WHERE t3.mysequence <= t1.mysequence
AND mynumber IS NOT NULL
)
) AS CALCULATED
FROM test t1;
-- below here it was only tested in SQLite3, but I believe it should
-- work on other DBMS since it uses standard/non-proprietary SQL
UPDATE test
SET mynumber = (
SELECT t2.mynumber
FROM test t2
WHERE t2.mysequence = (
SELECT MAX(t3.mysequence)
FROM test t3
WHERE t3.mysequence <= test.mysequence
AND mynumber IS NOT NULL
)
);