Select the last non-NULL value when current row is NULL - sql

Question

I know that there are a lot of solutions for this but unfortunately I cannot use partition or keyword TOP. Nothing I tried on earlier posts works.
My table looks like this:
The result I want is when any completion percentage is NULL it should get the value from last non-value completion percentage, like this:
I tried this query but nothing works. Can you tell me where I am going wrong?
SELECT sequence,project_for_lookup,
CASE WHEN completion_percentage IS NOT NULL THEN completion_percentage
ELSE
(SELECT max(completion_percentage) FROM [project_completion_percentage] AS t2
WHERE t1.project_for_lookup=t2.project_for_lookup and
t1.sequence<t2.sequence and
t2.completion_percentage IS NOT null
END
FROM [project_completion_percentage] AS t1

Answer 1

SQL Server 2008 doesn't support cumulative window functions. So, I would suggest outer apply:
select cp.projectname, cp.sequence,
coalesce(cp.completion_percentage, cp2.completion_percentage) as completion_percentage
from completion_percentage cp outer apply
(select top 1 cp2.*
from completion_percentage cp2
where cp2.projectname = cp.projectname and
cp2.sequence < cp.sequence and
cp2.completion_percentage is not null
order by cp2.sequence desc
) cp2;

Answer 2

Does this work? It seems to for me. You were missing a parenthesis and had the sequence backwards.
http://sqlfiddle.com/#!3/465f2/4
SELECT sequence,project_for_lookup,
CASE WHEN completion_percentage IS NOT NULL THEN completion_percentage
ELSE
(
SELECT max(completion_percentage)
FROM [project_completion_percentage] AS t2
WHERE t1.project_for_lookup=t2.project_for_lookup
-- sequence was reversed. You're on the row t1, and want t2 that is from a prior sequence.
and t2.sequence<t1.sequence
and t2.completion_percentage IS NOT null
--missing a closing paren
)
END
FROM [project_completion_percentage] AS t1