Question

The following code is probably self explanatory

Lists number of active subscribers 1st of june

select 
    count(subscribers) as activeSubscribers 
from subscriberlist sub 
where 
    to_date('2012-06', 'yyyy-mm') 
        between sub.firstDayOfSubscription and sub.lastDayOfSubscription

But if I want to get the number of subscribers in the beginning of every month the past year, what could I do (besides changing the date in the query and repeating).

Answer 1

You can generate a list of months as follows:

SELECT add_months (trunc (to_date('01/01/2012','MM/DD/YYYY'), 'MM'), 1*LEVEL -1) FirstDay
        FROM Dual
     CONNECT BY LEVEL <= MONTHS_BETWEEN(to_date('12/31/2012','MM/DD/YYYY'), to_date('01/01/2012','MM/DD/YYYY')) + 1
       ORDER BY FirstDay

This would give you the following output:

FIRSTDAY
--------
January, 01 2012 00:00:00+0000
February, 01 2012 00:00:00+0000
March, 01 2012 00:00:00+0000
April, 01 2012 00:00:00+0000
May, 01 2012 00:00:00+0000
June, 01 2012 00:00:00+0000
July, 01 2012 00:00:00+0000
August, 01 2012 00:00:00+0000
September, 01 2012 00:00:00+0000
October, 01 2012 00:00:00+0000
November, 01 2012 00:00:00+0000
December, 01 2012 00:00:00+0000

You can then include that query as an inline view as follows:

SELECT months.FirstDay,
       (SELECT count(subscribers)
          FROM subscriberlist sub
         WHERE months.FirstDay BETWEEN sub.firstDayOfSubscription AND sub.lastDayOfSubscription
       ) AS activeSubscribers
FROM (SELECT add_months(trunc (to_date('01/01/2012','MM/DD/YYYY'), 'MM'), 1*LEVEL -1) FirstDay
        FROM Dual
     CONNECT BY LEVEL <= MONTHS_BETWEEN(to_date('12/31/2012','MM/DD/YYYY'), to_date('01/01/2012','MM/DD/YYYY')) + 1
       ORDER BY FirstDay) Months

I’d probably wrap this in a sproc that accepts @startDate and @endDate parameters to define the date range you’re interested, but I followed your syntax with the date range being defined with strings.

I was playing with this using this SqlFiddle