Question

I have a sqlite database. I have three columns:_id, date, value.

I now want to extract a count of the _id:s depending on the day in the date, and calculate an average of the int value. This is for an Android app.

So I want to “select the day in date and for each day ( for sixty days), count how many _id:s there are for this day. Finally calculate the average of value.

I guess it is something like :

"SELECT DATE('now' 'days[i]') as date, COUNT(_id) as count,  AVG(value) as vl FROM v_efforts WHERE DATE(v_efforts.date) = DATE('now' 'days[i]')";

But I can’t get the 'days[i]' to work. I don’t know how i can get this value to increase to sixty, and then how I can store the count and vl for each of these sixty days.

THanks a lot!

Answer 1

You’ll want to use a GROUP BY expression to aggregate the entries by date. It’s not quite clear whether you’re looking for the last 60 days of entries in the database, or the entries from the last 60 real days (which would only be the same if you can assume that there are entries every day).

For the former (last 60 days which had database entries), you can use a LIMIT clause:

SELECT date,COUNT(_id),AVG(value) FROM v_efforts GROUP BY date ORDER BY date DESC LIMIT 60;

For the latter (last 60 real days), you can use WHERE:

SELECT date,COUNT(_id),AVG(value) FROM v_efforts WHERE date>DATE('now','-60 days') GROUP BY date ORDER BY date DESC;