Question

I have a postgresql table userDistributions like this :
user_id, start_date, end_date, project_id, distribution

I need to write a query in which a given date range and user id the output should be the sum of all distributions for every day for that given user.
So the output should be like this for input : ‘2-2-2012’ – ‘2-4-2012’, some user id :

Date SUM(Distribution)

2-2-2012 12
2-3-2012 15
2-4-2012 34


A user has distribution in many projects, so I need to sum the distributions in all projects for each day and output that sum against that day.

My problem is what I should group by against ? If I had a field as date (instead of start_date and end_date), then I could just write something like
select date, SUM(distributions) from userDistributions group by date;
but in this case I am stumped as what to do. Thanks for the help.

Answer 1

Use generate_series to produce your dates, something like this:

select dt.d::date, sum(u.distributions)
from userdistributions u
join generate_series('2012-02-02'::date, '2012-02-04'::date, '1 day') as dt(d)
  on dt.d::date between u.start_date and u.end_date
group by dt.d::date

Your date format is ambiguous so I guess while converting it to ISO 8601.