Count data per day in a specific month in Postgresql - postgresql

Question

I have a table with a create date called created_at and a delete date called delete_at for each record. If the record was deleted, the field save that date; it's a logic delete.
I need to count the active records in a specific month. To understand what is an active record for me, let's see an example:
For this example we'll use this hypothetical record:
id | created_at | deleted_at
1 | 23-01-2014 | 05-06-2014
This record is active for every days between its creation date and delete date. Including that last. So if I need count the active record for March, in this case, this record must be counted in every days of that month.
I have a query (really easy to do) that show the actives records for a specific month, but my principal problem is how to count that actives for each day in that month.
SELECT
date_trunc('day', created_at) AS dia_creacion,
date_trunc('day', deleted_at) AS dia_eliminacion
FROM
myTable
WHERE
created_at < TO_DATE('01-04-2014', 'DD-MM-YYYY')
AND (deleted_at IS NULL OR deleted_at >= TO_DATE('01-03-2014', 'DD-MM-YYYY'))

Answer 1

Here you are:
select
TO_DATE('01-03-2014', 'DD-MM-YYYY') + g.i,
count( case (TO_DATE('01-03-2014', 'DD-MM-YYYY') + g.i) between created_at and coalesce(deleted_at, TO_DATE('01-03-2014', 'DD-MM-YYYY') + g.i)
when true then 1
else null
end)
from generate_series(0, TO_DATE('01-04-2014', 'DD-MM-YYYY') - TO_DATE('01-03-2014', 'DD-MM-YYYY')) as g(i)
left join myTable on true
group by 1
order by 1;
You can add more specific condition for joining only relevant records from myTable, but even without it gives you idea how to achieve counting as desired.