Transposing number from one column into another one where = 0 - sql

Question

My question is this,
I have a query I'm working on and I have some values that are 0. I want to be able to take a value from a previous month that is not zero and put it in place of the zero. See the example below.
SELECT item,
stock,
sold,
level,
month,
year
FROM agingdata
GROUP BY item,
stock,
sold,
month,
year,
level
HAVING ( item = #Item )
ORDER BY year,
month
So I want take the number 2455 and input it into the stock where it says 0, taking last months balance number as the current months stock level. Is that even possible?

Answer 1

You can find the previous non-zero level per item (for zero level items) using this query:
SELECT find.item, find.month, find.year, result.level
FROM AgingData result
JOIN (
SELECT original.item, original.month, original.year, max(cast(cast(previous.year as varchar) + '-' + cast(previous.month as varchar) + '-1' as datetime)) previous_date
FROM AgingData original
JOIN AgingData previous
ON original.item = previous.item
AND ((original.year > previous.year)
OR (original.year = previous.year AND original.month > previous.month))
WHERE original.level = 0
AND previous.level != 0
GROUP BY original.item, original.month, original.year ) find
ON result.item = find.item
AND cast(cast(result.year as varchar) + '-' + cast(result.month as varchar) + '-1' as datetime) = find.previous_date
This will work even if the previous non-zero level is several months before.

Answer 2

Something along these lines, this only works if the previous month is non-zero....
SELECT cur.Item,
CASE
WHEN (cur.Stock<>0)
THEN cur.Stock
ELSE prev.Stock
END as Stock,
cur.Sold,
cur.Level,
cur.Month,
cur.Year
FROM AgingData cur
LEFT OUTER JOIN AgingData prev
ON prev.item=cur.item and prev.Month = cur.Month - 1
GROUP BY cur.Item, cur.Stock, cur.Sold, cur.Month, cur.Year, cur.Level
HAVING (cur.Item = #Item)
ORDER BY cur.Year, cur.Month