Get average of last 7 days - sql

Question

I'm attacking a problem, where I have a value for a a range of dates. I would like to consolidate the rows in my table by averaging them and reassigning the date column to be relative to the last 7 days. My SQL experience is lacking and could use some help. Thanks for giving this a look!!
E.g.
7 rows with dates and values.
UniqueId Date Value
........ .... .....
a 2014-03-20 2
a 2014-03-21 2
a 2014-03-22 3
a 2014-03-23 5
a 2014-03-24 1
a 2014-03-25 0
a 2014-03-26 1
Resulting row
UniqueId Date AvgValue
........ .... ........
a 2014-03-26 2
First off I am not even sure this is possible. I'm am trying to attack a problem with this data at hand. I thought maybe using a framing window with a partition to roll the dates into one date with the averaged result, but am not exactly sure how to say that in SQL.

Answer 1

Am taking following as sample
CREATE TABLE some_data1 (unique_id text, date date, value integer);
INSERT INTO some_data1 (unique_id, date, value) VALUES
( 'a', '2014-03-20', 2),
( 'a', '2014-03-21', 2),
( 'a', '2014-03-22', 3),
( 'a', '2014-03-23', 5),
( 'a', '2014-03-24', 1),
( 'a', '2014-03-25', 0),
( 'a', '2014-03-26', 1),
( 'b', '2014-03-01', 1),
( 'b', '2014-03-02', 1),
( 'b', '2014-03-03', 1),
( 'b', '2014-03-04', 1),
( 'b', '2014-03-05', 1),
( 'b', '2014-03-06', 1),
( 'b', '2014-03-07', 1)
OPTION A : - Using PostgreSQL Specific Function WITH
with cte as (
select unique_id
,max(date) date
from some_data1
group by unique_id
)
select max(sd.unique_id),max(sd.date),avg(sd.value)
from some_data1 sd inner join cte using(unique_id)
where sd.date <=cte.date
group by cte.unique_id
limit 7
> SQLFIDDLE DEMO
OPTION B : - To work in PostgreSQL and MySQL
select max(sd.unique_id)
,max(sd.date)
,avg(sd.value)
from (
select unique_id
,max(date) date
from some_data1
group by unique_id
) cte inner join some_data1 sd using(unique_id)
where sd.date <=cte.date
group by cte.unique_id
limit 7
> SQLFDDLE DEMO

Answer 2

Maybe something along the lines of SELECT AVG(Value) AS 'AvgValue' FROM tableName WHERE Date BETWEEN dateStart AND dateEnd That will get you the average between those dates and you have dateEnd already so you could use that result to create the row you're looking for.

Answer 3

For PostgreSQL a window function might be what you want:
DROP TABLE IF EXISTS some_data;
CREATE TABLE some_data (unique_id text, date date, value integer);
INSERT INTO some_data (unique_id, date, value) VALUES
( 'a', '2014-03-20', 2),
( 'a', '2014-03-21', 2),
( 'a', '2014-03-22', 3),
( 'a', '2014-03-23', 5),
( 'a', '2014-03-24', 1),
( 'a', '2014-03-25', 0),
( 'a', '2014-03-26', 1),
( 'a', '2014-03-27', 3);
WITH avgs AS (
SELECT unique_id, date,
avg(value) OVER w AS week_avg,
count(value) OVER w AS num_days
FROM some_data
WINDOW w AS (
PARTITION BY unique_id
ORDER BY date
ROWS BETWEEN 6 PRECEDING AND CURRENT ROW))
SELECT unique_id, date, week_avg
FROM avgs
WHERE num_days=7
Result:
unique_id | date | week_avg
-----------+------------+--------------------
a | 2014-03-26 | 2.0000000000000000
a | 2014-03-27 | 2.1428571428571429
Questions include:
What happens if a day from the preceding six days is missing? Do we want to add it and count it as zero?
What happens if you add a day? Is the result of the code above what you want (a rolling 7-day average)?

Answer 4

For SQL Server, you can follow the below approach. Try this
1. For weekly value's average
SET DATEFIRST 4
;WITH CTE AS
(
SELECT *,
DATEPART(WEEK,[DATE])WK,
--Find last day in that week
ROW_NUMBER() OVER(PARTITION BY UNIQUEID,DATEPART(WEEK,[DATE]) ORDER BY [DATE] DESC) RNO,
-- Find average value of that week
AVG(VALUE) OVER(PARTITION BY UNIQUEID,DATEPART(WEEK,[DATE])) AVGVALUE
FROM DATETAB
)
SELECT UNIQUEID,[DATE],AVGVALUE
FROM CTE
WHERE RNO=1
Click here to view result
2. For last 7 days value's average
DECLARE #DATE DATE = '2014-03-26'
;WITH CTE AS
(
SELECT UNIQUEID,[DATE],VALUE,#DATE CURRENTDATE
FROM DATETAB
WHERE [DATE] BETWEEN DATEADD(DAY,-7,#DATE) AND #DATE
)
SELECT UNIQUEID,CURRENTDATE [DATE],AVG(VALUE) AVGVALUE
FROM CTE
GROUP BY UNIQUEID,CURRENTDATE
Click here to view result