Showing Monthly Totals from Multiple Columns in PostgreSQL - sql

Question

I am looking to see the number of firstexam patients seen per month for a given date range this year vs last year, and compare that to the total number of patients seen per month for the same date range.
I am able to set up the firstexam patients as follows:
select case EXTRACT(month FROM patient_info.firstexam)
when 1 then '01 - January'
when 2 then '02 - February'
when 3 then '03 - March'
when 4 then '04 - April'
when 5 then '05 - May'
when 6 then '06 - June'
when 7 then '07 - July'
when 8 then '08 - August'
when 9 then '09 - September'
when 10 then '10 - October'
when 11 then '11 - November'
when 12 then '12 - December'
end as month,
sum(case when patient_info.firstexam >= '2013-01-01' AND patient_info.firstexam <= '2013-12-31' then 1 else 0 end) thisyear,
sum(case when patient_info.firstexam >= '2012-01-01' AND patient_info.firstexam <= '2012-12-31' then 1 else 0 end) lastyear
from patient_info WHERE (patient_info.firstexam >= '2013-01-01' AND patient_info.firstexam <= '2013-12-31' OR patient_info.firstexam >= '2012-01-01' AND patient_info.firstexam <= '2012-12-31')
GROUP BY month
ORDER BY month
This gives me three columns: month, thisyear, lastyear.
Please note: I entered numerical month before month name because I could not get the months to appear in chronological order otherwise. Any hints to not show the number before the month would be appreciated.
I would like to add two more columns for total patients - something like:
select case EXTRACT(month FROM patient_info.lastexam)
when 1 then '01 - January'
when 2 then '02 - February'
when 3 then '03 - March'
when 4 then '04 - April'
when 5 then '05 - May'
when 6 then '06 - June'
when 7 then '07 - July'
when 8 then '08 - August'
when 9 then '09 - September'
when 10 then '10 - October'
when 11 then '11 - November'
when 12 then '12 - December'
end as month,
sum(case when patient_info.lastexam >= '2013-01-01' AND patient_info.lastexam <= '2013-12-31' then 1 else 0 end) totalthisyear,
sum(case when patient_info.lastexam >= '2012-01-01' AND patient_info.lastexam <= '2012-12-31' then 1 else 0 end) totallastyear
from patient_info WHERE (patient_info.lastexam >= '2013-01-01' AND patient_info.lastexam <= '2013-12-31' OR patient_info.lastexam >= '2012-01-01' AND patient_info.lastexam <= '2012-12-31')
GROUP BY month
ORDER BY month
with the results in 5 columns: month, thisyear, totalthisyear, lastyear, totallastyear
but can't seem to figure out exactly how this could be done. The order of the columns is not important.
It could be: month, thisyear, lastyear, totalthisyear, totallastyear

Answer 1

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