Finding Avg of following dataset - sql

Question

Following is the data.
select * from (
select to_date('20140601','YYYYMMDD') log_date, null weight from dual
union
select to_date('20140601','YYYYMMDD')+1 log_date, 0 weight from dual
union
select to_date('20140601','YYYYMMDD')+2 log_date, 4 weight from dual
union
select to_date('20140601','YYYYMMDD')+3 log_date, 4 weight from dual
union
select to_date('20140601','YYYYMMDD')+4 log_date, null weight from dual
union
select to_date('20140601','YYYYMMDD')+5 log_date, 8 weight from dual);
Log_date weight avg_weight
----------------------------------
6/1/2014 NULL 0 (0/1) Since no previous data, I consider it as 0
6/2/2014 0 0 ((0+0)/2)
6/3/2014 4 4/3 ((0+0+4)/3)
6/4/2014 4 2 (0+0+4+4)/4
6/5/2014 NULL 2 (0+0+4+4+2)/5 Since it is NULL I want to take previous day avg = 2
6/6/2014 8 3 (0+0+4+4+2+8)/6 =3
So the average for the above data should be 3.
How can I achieve this in SQL instead of PLSQL. Appreciate any help on this.

Answer 1

I just learned how to use recursive CTEs today, really excited! Hope this helps...
; WITH RawData (log_Date, Weight) AS (
select cast('2014-06-01' as SMALLDATETIME)+0, null
UNION ALL select cast('2014-06-01' as SMALLDATETIME)+1, 0
UNION ALL select cast('2014-06-01' as SMALLDATETIME)+2, 4
UNION ALL select cast('2014-06-01' as SMALLDATETIME)+3, 4
UNION ALL select cast('2014-06-01' as SMALLDATETIME)+4, null
UNION ALL select cast('2014-06-01' as SMALLDATETIME)+5, 8
)
, IndexedData (Id, log_Date, Weight) AS (
SELECT ROW_NUMBER() OVER (ORDER BY log_Date)
, log_Date
, Weight
FROM RawData
)
, ResultData (Id, log_Date, Weight, total, avg_weight) AS (
SELECT Id
, log_Date
, Weight
, CAST(CASE WHEN Weight IS NULL THEN 0 ELSE Weight END AS FLOAT)
, CAST(CASE WHEN Weight IS NULL THEN 0 ELSE Weight END AS FLOAT)
FROM IndexedData
WHERE Id = 1
UNION ALL
SELECT i.Id
, i.log_Date
, i.Weight
, CAST(r.total + CASE WHEN i.Weight IS NULL THEN r.avg_weight ELSE i.Weight END AS FLOAT)
, CAST(r.total + CASE WHEN i.Weight IS NULL THEN r.avg_weight ELSE i.Weight END AS FLOAT) / i.Id
FROM ResultData r
JOIN IndexedData i ON i.Id = r.Id + 1
)
SELECT Log_Date, Weight, avg_weight FROM ResultData
OPTION (MAXRECURSION 0)
This gives the output:
Log_Date Weight avg_weight
----------------------- ----------- ----------------------
2014-06-01 00:00:00 NULL 0
2014-06-02 00:00:00 0 0
2014-06-03 00:00:00 4 1.33333333333333
2014-06-04 00:00:00 4 2
2014-06-05 00:00:00 NULL 2
2014-06-06 00:00:00 8 3
Note that in my answer, I modified the "Data" section of your question as it didn't compile for me. It's still the same data though, hope it helps.
Edit: By default, MAXRECURSION is set to 100. This means that the query will not work for more than 101 rows of Raw Data. By adding the OPTION (MAXRECURSION 0), I have removed this limit so that the query works for all input data. However, this can be dangerous if the query isn't tested thoroughly because it might lead to infinite recursion.