Group by month and name SQL - sql

Question

I need some help with SQL.
I have
Table1 with columns Id, Date1 and Date2
Table2 with columns Table1Id and Table2Id
Table3 with columns Id and Name
Here is my try:
with tmp_tab as (
select
v."Name" as name
, date_part('month', cv."OfferAcceptedDate") as MonthAcceptedName
, date_part('month', cv."OfferSentDate") as MonthSentName
, 1 as cntAcc
, 1 as cntSent
from hr_metrics."CvInfo" as cv
join hr_metrics."CvInfoVacancy" as civ
on civ."CvInfosId" = cv."Id"
join hr_metrics."Vacancy" as v
on civ."VacanciesId" = v."Id"
where cv."OfferSentDate" is not null
and date_part('year', cv."OfferSentDate") = date_part('year', CURRENT_DATE)
group by v."Name" , date_part('month', cv."OfferAcceptedDate"),
date_part('month', cv."OfferSentDate")
)
select distinct
tmp_tab."name" as name,
tmp_tab.MonthSentName as mSent,
tmp_tab.MonthAcceptedName as mAcc,
Sum(tmp_tab.cntSent) as sented,
Sum(tmp_tab.cntacc) as accepted
from tmp_tab as tmp_tab
group by tmp_tab.name, tmp_tab.MonthSentName, tmp_tab.MonthAcceptedName;
I need to take Count(date2)/Count(date1) grouped by monthes and name.
I have no idea how to do that, as there is no table with monthes.
DB - Postgres
sample data from comment:
t1
1 | 01/01/2021 | 31/03/2021
2 | 05/01/2021 | 18/01/2021
3 | 12/01/2021 | 31/01/2021
4 | 13/03/2021 | 22/03/2021
t2
1 | 1
2 | 1
3 | 2
4 | 1
t3
1 | SomeName1
2 | someName2
Desired result:
Name | month | value
SomeName1 | 1 | 1\2
SomeName1 | 3 | 2
SomeName2 | 1 | 1
Update: if count(date2) == 0, than count(date2) = -1

Answer 1

Source answer
Here code for my question thats work. And yeah, i've asked it on ru too.
select name, month, sum((SRC=1)::int) as AcceptedCount, sum((SRC=2)::int) as SentCount,
case when sum((SRC=1)::int) = 0 then -1
else sum((SRC=2)::int)::float / sum((SRC=1)::int) end as Result
from (
select v.name, SRC,
extract('month' from case SRC when 1 then OfferAcceptedDate else OfferSentDate end) as month
from (select (date_part('year', CURRENT_DATE)::char(4) || '-01-01')::timestamptz as from_date) x
cross join (select 1 as SRC union all select 2) s
join CvInfo as cv on (SRC=1 and cv.OfferAcceptedDate >= from_date and cv.OfferAcceptedDate < from_date + interval '1 year')
or (SRC=2 and cv.OfferSentDate >= from_date and cv.OfferSentDate < from_date + interval '1 year')
join CvInfoVacancy as civ on civ.CvInfosId = cv.Id
join Vacancy as v on civ.VacanciesId = v.Id
where case SRC when 1 then OfferAcceptedDate else OfferSentDate end is not null
) x
group by name, month