There is no need to create a range to make an overlap:
select to_char(d, 'YYYY-MM') as "Month", e.name
from
(
select generate_series(
'2013-01-01'::date, '2013-05-01', '1 month'
)::date
) s(d)
inner join
employee e on
date_trunc('month', e.start_date)::date <= s.d
and coalesce(e.finish_date, 'infinity') > s.d
order by 1, 2
If you want the months with no active employees to show then change the inner
for a left join
Erwin, about your comment:
the second expression would have to be coalesce(e.finish_date, 'infinity') >= s.d
Notice the requirement:
So if I have an employee who worked for 4 months eg. from 01/01/2013 to 01/05/2013 I'll have him in four months
From that I understand that the last active day is indeed the previous day from finish.
If I use your "fix" I will include employee f
in month 05
from my example. He finished in 2013-05-01
:
('f', '2013-04-17', '2013-05-01'),