SQL Server: How to add all dates of the month?
Use a function like this one, from my answer to Get a list of dates between two dates using a function:

CREATE FUNCTION dbo.ExplodeDates(@startdate datetime, @enddate datetime)
returns table as
return (
with 
 N0 as (SELECT 1 as n UNION ALL SELECT 1)
,N1 as (SELECT 1 as n FROM N0 t1, N0 t2)
,N2 as (SELECT 1 as n FROM N1 t1, N1 t2)
,N3 as (SELECT 1 as n FROM N2 t1, N2 t2)
,N4 as (SELECT 1 as n FROM N3 t1, N3 t2)
,N5 as (SELECT 1 as n FROM N4 t1, N4 t2)
,N6 as (SELECT 1 as n FROM N5 t1, N5 t2)
,nums as (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 1)) as num FROM N6)
SELECT DATEADD(day,num-1,@startdate) as thedate
FROM nums
WHERE num &lt;= DATEDIFF(day,@startdate,@enddate) + 1
);


...and query it like:

SELECT *
FROM YourTable t
CROSS APPLY dbo.ExplodeDates(
    DATEFROMPARTS(t.[Year], t.[Month], 1), 
    EOMONTH(DATEFROMPARTS(t.[Year], t.[Month], 1))
) AS d;