如何在两个日期之间激活数字

Question

我有以下模式：

name | hire_date                   | last_date                   | active
n1   | January 20, 2018, 12:00 AM  |                             | true
n2   | October 1, 2018, 12:00 AM   | February 18, 2020, 12:00 AM | false
n3   | October 15, 2018, 12:00 AM  |                             | true
n4   | January 12 2019, 12:00 AM   |                             | true
n5   | February 12, 2019, 12:00 AM |                             | true
n6   | December 12, 2019, 12:00 AM | January 15, 2020, 12:00 AM  | false
n7   | February 17, 2020, 12:00 AM |                             | true

我需要提取active员工总数的每月计数。

我正在尝试将表本身连接起来，并获得行数，但不确定如何进行：

select 
-- ot1.name, ot2.name, ot1.hire_date, ot2.hire_date, ot1.last_date, ot2.last_date, 
date_trunc('month', ot1.hire_date) AS hire_dates, count(ot1.hire_date)
from ops_teammates ot1
join ops_teammates ot2 ON ot1.hire_date >= ot2.hire_date 
group by hire_dates
order by ot1.hire_date, ot2.hire_date; 

我怎样才能得到像一样的计数

Jan 2018, 1
Oct 2018, 3
Jan 2019, 4
Feb 2019, 5
Dec 2019, 6
Jan 2020, 5
Feb 2020, 5

Answer 1

您可以使用union all和聚合：：

select month_start, sum(cnt),
sum(sum(cnt)) over (order by month_start) as running_cnt
from (
select 1 cnt, date_trunc('month', hire_date) month_start from ops_teammates 
union all
select -1, date_trunc('month', last_date) + interval '1 month' from ops_teammates  where last_date is not null
)
group by month_start
order by month_start