How can I get weekly sales for every salesman - postgresql

Question

I have a table like below (tablename: sales)
sales_datetime
sales
salesman
2022-08-01 09:00:00
100
John
2022-08-01 11:00:00
200
John
2022-08-02 10:00:00
100
Peter
2022-08-02 13:00:00
300
John
2022-08-04 14:00:00
300
Peter
2022-08-05 12:00:00
100
John
2022-08-05 16:00:00
200
John
From that table I want to make a summary sales for 5 days period for each salesman. So the summary table that I want is look like this
periode
total_sales
salesman
2022-08-01
300
John
2022-08-01
0
Peter
2022-08-02
300
John
2022-08-02
100
Peter
2022-08-03
0
John
2022-08-03
0
Peter
2022-08-04
0
John
2022-08-04
300
Peter
2022-08-05
300
John
2022-08-05
0
Peter
I have created following query (PSQL) but the results were not same as I want. Assume today is 2022-08-05
with dateseries as
(select generate_series(current_date-'4 days'::interval,
current_date::date,
'1 day'::interval)::date as periode)
select d.periode,coalesce(sum(s.sales),0) as total_sales,s.salesman from dateseries d
left outer join sales s
on d.periode=s.sales_datetime::date
group by d.periode, s.salesman order by d.periode
results:
periode
total_sales
salesman
2022-08-01
300
John
2022-08-02
300
John
2022-08-02
100
Peter
2022-08-03
0
(NULL)
2022-08-04
300
Peter
2022-08-05
300
John
Any advices would be so great. Thank you

Answer 1

Step by step first aggregate the daily sales per salesperson (aggregated_sales CTE), create a list of days to report (days CTE), create a list of salesmen (salesmen CTE) and then query the sales for each day/salesman pair.
with aggregated_sales as
(
select sales_datetime::date sales_date, sum(sales) sales, salesman
from sales group by sales_datetime::date, salesman
),
days(sales_date) as
(
select d::date
from generate_series('2022-08-01', '2022-08-08', interval '1 day') d
),
salesmen (salesman) as
(
select distinct salesman from sales
)
select sales_date, coalesce(sales, 0) sales, salesman
from (select * from days cross join salesmen) fl
left outer join aggregated_sales ags using (sales_date, salesman);
The query may be shorter if CTEs are inlined yet I think that clarity and readability are more important than mere size.
In order to "make a summary sales for 5 days period for each salesman" replace generate_series('2022-08-01', '2022-08-08', interval '1 day') with generate_series(current_date - 4, current_date, interval '1 day').

Answer 2

the results were not same as I want. Assume today is 2022-08-05
Please note that '2022-08-05'::date - '5 days'::interval will give you 2022-07-31, and not 2022-08-01 as you assume. Because of that, I think you meant it to be current_date - '4 days'::interval.
With that out of the way, here is one possible query:
with sales_by_date as (
select
salesman,
sales_datetime::date,
sum(sales) total_sales
from sales
where
-- assuming you need to have totals for salesmen that had sales in specified period only
sales_datetime::date between current_date-'4 days'::interval and current_date
group by
salesman,
sales_datetime::date),
dateseries as (
select
distinct salesman,
generate_series(current_date-'4 days'::interval, current_date, '1 day'::interval)::date as periode
from sales_by_date)
select
d.periode,
coalesce(s.total_sales, 0) total_sales,
d.salesman
from dateseries d
left join sales_by_date s
on d.periode = s.sales_datetime
and d.salesman = s.salesman
order by d.periode, d.salesman;
But you still have to figure out some requirements for this problem. E.g. what if for the specified period there are no sales at all in the sales table?