SQL Fiddle
select
to_char(('2012-' || m || '-01')::date, 'Month'),
thisyear, lastyear, totalthisyear, totallastyear
from (
select
extract(month from m) as m,
sum(case
when firstexam between '2013-01-01' and '2013-12-31' then firstexam_count
else 0 end
) as thisyear,
sum(case
when firstexam between '2012-01-01' and '2012-12-31' then firstexam_count
else 0 end
) as lastyear,
sum(case
when lastexam between '2013-01-01' and '2013-12-31' then lastexam_count
else 0 end
) as totalthisyear,
sum(case
when lastexam between '2012-01-01' and '2012-12-31' then lastexam_count
else 0 end
) as totallastyear
from
generate_series (
'2012-01-01'::date, '2013-12-31', '1 month'
) g(m)
left join (
select count(*) as firstexam_count, date_trunc('month', firstexam) as firstexam
from patient_info
where firstexam between '2012-01-01' and '2013-12-31'
group by 2
) pif on firstexam = m
left join (
select count(*) as lastexam_count, date_trunc('month', lastexam) as lastexam
from patient_info
where lastexam between '2012-01-01' and '2013-12-31'
group by 2
) pil on lastexam = m
group by 1
) s
order by m
