Question

I’ve just started learning SQLite, and had a question.

Here is an example of what I mean.

This is my CSV:

date
2010-10-24
2010-10-31
2010-11-01
2011-02-14
2011-02-15
2011-02-16
2011-10-01
2012-01-15
2012-05-12
2012-05-14
2012-08-12
2012-08-26

My code:

SELECT STRFTIME('%Y-%m', date) AS 'month', COUNT() AS 'month_count'
    FROM tableName 
    GROUP BY STRFTIME('%Y-%m', date);

The result (in comma-delimited form):

month, month_count
2010-10, 2
2010-11, 1
2011-02, 3
2011-10, 1
2012-01, 1
2012-05, 2
2012-08, 2

What I’m looking for now, is a way to get the average number of ‘month_count’ per month, which is of course different from just the average of ‘month_count’. That is, the former equals 0.55, while the latter equals 1.71, and I’m trying ti calculate the former.

I tried using AVG(COUNT()), though that obviously made no logical sense.

I’m guessing I’d have to store the code-generated table as a temporary file, then get the average from it, though I’m not sure how to properly write it.

Does anyone know what I’m missing?

Answer 1

Try the code below:

create table test(date date);
insert into test values ('2010-10-24');
insert into test values ('2010-10-31');
insert into test values ('2010-11-01');
insert into test values ('2011-02-14');
insert into test values ('2011-02-15');
insert into test values ('2011-02-16');
insert into test values ('2011-10-01');
insert into test values ('2012-01-15');
insert into test values ('2012-05-12');
insert into test values ('2012-05-14');
insert into test values ('2012-08-12');
insert into test values ('2012-08-26');

SELECT a.tot_months 
     , b.month_diff
     , cast(a.tot_months as float) / b.month_diff avg_count
  FROM (SELECT COUNT(*) tot_months FROM test) a
     , (SELECT cast((strftime('%m',max(date))+12*strftime('%Y',max(date))) as int) -
               cast((strftime('%m',min(date))+12*strftime('%Y',min(date))) as int) as 'month_diff'
          FROM test) b
;

Output:

C:\scripts>sqlite3 < foo.sql
12|22|0.545454545454545