sql - 显示PostgreSQL中多个列的每月总计

我希望看到今年与去年相比，给定日期范围内每月就诊的初诊患者数量，并将其与相同日期范围内每月就诊的患者总数进行比较。
我可以设置如下的第一次检查患者：

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

这给了我三栏：月，今年，去年。
请注意：我在月份名称之前输入了数字月份，因为否则无法按时间顺序显示月份。如有任何不在本月前显示号码的提示，将不胜感激。
我想再加上两个列来表示全部患者，比如：

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

结果分为5列：月、今年、今年、去年、去年
但似乎不知道怎么做。列的顺序并不重要。
可能是：月，今年，去年，今年，去年

最佳答案

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

关于sql - 显示PostgreSQL中多个列的每月总计，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/25139715/