PHP Database take average and counter

I have a database that has this

Date       -   Temp

2013-12-01 -   12    
2013-12-31 -   18
Copy code

Holds 1 month. Im graphing this by JSON in my PHP page. But I want something different, to graph it weekly. Like It will take each 7 days temp average and if I find a suitable sql statement for it, it would be great.

I found this in my pdf.

SELECT Date,Temp COUNT(Date) AS weekly, AVG(Temp) AS Temperature 
    FROM temp2 GROUP BY Date ORDER BY Date;
Copy code

But it will take all the 31 days which is not weekly but monthly.

Anyways, is there something you can do?

Thanks.