SQLite query to join on a range of dates?

Question

I am working with SQLite.

Suppose I have a table sales with two columns, date and count, to keep track of how many glasses of lemo

Answer 1

I think you need something like this:

SELECT sum(count) / ((strftime('%s','2010-01-10')-strftime('%s','2010-01-04')+86400)/86400)
FROM sales
WHERE date IS BETWEEN '2010-01-04' AND '2010-01-10';

The query calculates the exact number of days by taking the seconds between the given dates
and dividing with 86400 (= 24*3600) secs.

For example

SELECT (strftime('%s','2010-03-01')-strftime('%s','2010-01-01') + 86400) / 86400

outputs 60 which is the correct value.

Check out SQLite's Date And Time Functions.

Answer 2

Create a calendar table and join onto that:

Something like this will do:

create table dates (id integer primary key);
insert into dates default values;
insert into dates default values;
insert into dates select null from dates d1, dates d2, dates d3 , dates d4;
insert into dates select null from dates d1, dates d2, dates d3 , dates d4;
alter table dates add date datetime;
update dates set date=date('2000-01-01',(-1+id)||' day');

That will cover you till 2287-05-20 Adding an index to the date column in the dates table won't hurt. My sqlite is little rusty, so I suggest you consult the manual on that.

Edit: Code for the index:

create unique index ux_dates_date on dates (date);

Answer 3

You could use a Recursive Common Table expression to generate a series of dates and join to it:

WITH RECURSIVE
  cnt(x) AS (
    SELECT 0
    UNION ALL
    SELECT x+1 FROM cnt
    LIMIT (SELECT ((julianday('2010-01-10') - julianday('2010-01-04'))) + 1)
), 
WITH date_series AS (
  SELECT date(julianday('2010-01-04'), '+' || x || ' days') as date 
FROM date_series ds
)
SELECT AVG(COALESCE(s.count, 0)) as avg_sales_count
FROM date_series ds
  LEFT JOIN sales s ON ds.date = s.date

I wrote a blog post with more info here: http://www.geekytidbits.com/generate-date-range-sqlite/