Merging two SELECT queries with same date fields - sql

Question

I have a table of Tasks where I have records for a particular date. I want to have all dates in one month displayed with numbers of tasks per date. If on some date there were no record of a task it should be written 0.
I have results with duplicating records from the same date when there were tasks on a given day.
Table:
Date Tasks
2021-08-01 0
2021-08-02 0
2021-08-03 0
2021-08-03 25
2021-08-04 0
2021-08-04 18
2021-08-05 0
2021-08-05 31
2021-08-06 0
SQL code I am using:
Declare #year int = 2021, #month int = 8;
WITH numbers
as
(
Select 1 as value
UNion ALL
Select value +1 from numbers
where value + 1 <= Day(EOMONTH(datefromparts(#year, #month, 1)))
)
SELECT datefromparts(#year, #month, numbers.value) AS 'Datum', 0 AS 'Tasks' FROM numbers
UNION
SELECT CONVERT(date, added_d) AS 'Datum', COUNT(*) AS 'Tasks' FROM Crm.Task
WHERE YEAR(added_d) = '2021' AND MONTH(added_d) = '8' GROUP BY CONVERT(date, added_d)
How can I remove duplicates that I will have only one date record 21-08-03 with 25 tasks?
Thank you for your help

Answer 1

You requires OUTER JOIN :
WITH numbers as (
Select datefromparts(#year, #month, 1) as value
UNION ALL
Select DATEADD(DAY, 1, value) as value
from numbers
where value < EOMONTH(value)
)
select num.value, COUNT(tsk.added_d) AS Tasks
from numbers num left join
Crm.Task tsk
on CONVERT(date, tsk.added_d) = num.value
GROUP BY num.value;

Answer 2

If you want all dates for one month, you can do:
with dates as (
select datefromparts(#year, #month, 1) as dte
union all
select dateadd(day, 1, dte)
from dates
where dte < eomonth(dte)
)
You can then incorporate this into the logic using an outer join or subquery:
with dates as (
select datefromparts(#year, #month, 1) as dte
union all
select dateadd(day, 1, dte)
from dates
where dte < eomonth(dte)
)
select d.dte, count(t.added_d)
from dates d left join
Crm.Task t
on convert(date, t.added_d) = d.dte
group by d.dte
order by d.dte;
You can easily extend the logic for the CTE for more than one month, by adjusting the where clause in the second clause.