SQL moving average with calc of average price per square metre - sql

Question

I'm trying to get a moving average for a set of real estate data that I can then graph, using MS SQL 2005.
Fields are: DateSold datetime, FloorSQM decimal(8,2), Price decimal(10,0)
What I need to do is get an average price per square metres of all the properties sold within each month as far back as we have data, which can be several years.
Therefore I need to Price/FloorSQM each property, and then apply a moving average to them for each month. Hope that makes sense.
I am completely stuck trying to figure this out, and googling endlessly is endlessly confusing.
I thought I found what I'm looking for in another post, but I keep getting "incorrect syntax near 'm'" when I try to compile it.
SELECT YEAR(DateSold) AS year,
MONTH(DateSold) AS month,
ROUND(Euros/CONVERT(DECIMAL(10,2),FloorSQM),2) as avg
FROM
(select s.*, DATE_ADD(DTE, INTERVAL m.i MONTH) DateSold, m.i
FROM Property s
cross join (select 0 i union select 1 union select 2 union select 3 union
select 4 union select 5 union select 6 union select 7 union
select 8 union select 9 union select 10 union select 11) m) sq
WHERE DateSold <= curdate()
GROUP BY YEAR(DateSold), MONTH(DateSold)
When I have this working, I then need to introduce a WHERE clause so I can limit the properties found to certain kinds (houses, apartments) and areas (New York, Los Angeles, etc)
Can anyone lend a hand please? Many thanks for your help.

Answer 1

This should run, you were using some Mysql syntax:
SELECT YEAR(DateSold) AS year,
MONTH(DateSold) AS month,
ROUND(Euros/CONVERT(DECIMAL(10,2),FloorSQM),2) as avg
FROM (SELECT s.*, DATEADD(MONTH,m.i,DateSold) DateSold2, m.i
FROM Property s
cross join (select 0 i union select 1 union select 2 union select 3 union
select 4 union select 5 union select 6 union select 7 union
select 8 union select 9 union select 10 union select 11
) m
)sq
WHERE DateSold<= GETDATE()
GROUP BY YEAR(DateSold), MONTH(DateSold)
Not sure if it returns the desired results.
Update: I thought DTE was a field name, you can't have DateSold referenced twice in your subquery, so I changed to DateSold2, not sure if you intend for the DATEADD() result to be used in all places where DateSold is used, you could also just remove DateSold from your subquery SELECT list.

Answer 2

Try this:
SELECT YEAR(DateSold) AS year,
MONTH(DateSold) AS month,
AVG(ROUND(Price/CONVERT(DECIMAL(10,2),FloorSQM),2)) as avg
FROM property p
GROUP BY YEAR(DateSold), MONTH(DateSold);
Note, changed the query from Euros to Price, as you specified in the schema.
The grouping of year, month is all you need to get the average of the price for that month. You were missing the aggregate function, AVG around your formula (though might be more accurate if ROUND was wrapped around AVG). I set up a quick sample at SQLFiddle.