Conditional scoring - sql-server

Question

I have a table that shows only the 'captured' data. For example in the below exhibit, the emp_no 17 has 2 records - for November and February (for a specified 6 month period, from July 2017). It does not have data for the other 4 months (within the 6-month date range, from previous 6 months to current date).
How can I populate these missing months (Sept, Oct, Dec) with default values for num_differences of 0 for the missing months? (for example, in this case, I want emp_no 17 to have the below (I can ignore 2018 data - only require data up to Dec 2017):
I have the script below:
declare #YMN date;
set #YMN = '20171201';
DECLARE #Emp TABLE (
[date] date,
[emp_no] int,
[num_differences] int
);
INSERT INTO #Emp VALUES
('2017-09-14', 17, 1), ('2017-12-01', 17, 1),('2017-12-18', 17, 1),('2017-12-21', 17, 1),
('2017-09-27', 17, 1), ('2017-12-04', 17, 1);
-------------------------------------------------------------------------------------------get missing dates---------------------------------------------------------------------------
;WITH cte_Emp_No AS (
SELECT DISTINCT [emp_no]
FROM #Emp
),
cte_dates AS (
SELECT [emp_no], DATEADD(month, -6, DATEADD(dd, -(DAY(dateadd(month, 1, #YMN)) - 1), dateadd(month, 1, #YMN))) AS [date]
FROM cte_Emp_No
UNION ALL
SELECT [emp_no], DATEADD(month, 1, [date]) AS [date]
FROM cte_dates
WHERE [date] < dateadd(month, 0, #YMN)
)
SELECT DISTINCT ISNULL(e.emp_no, c.emp_no) emp_no, ISNULL(e.date, c.date) date, ISNULL(e.num_differences, 0) num_differences
into ##new_table
FROM #Emp AS e
RIGHT JOIN cte_dates AS c ON YEAR(c.date) = YEAR(e.date) AND MONTH(c.date) = MONTH(e.date)
-----------------------------------------------------------------------------------------------MAIN CTE------------------------------------------------------------------------------
;with cte_RawScore as
(
select emp_no
, date YMN
,sum(case when datediff(month, convert(datetime, #YMN, 112), date) = 0 then num_differences else 0 end) as thismonth
,sum(case when datediff(month, convert(datetime, #YMN, 112), date) between -2 and 0 then num_differences else 0 end) as last3month
,sum(case when datediff(month, convert(datetime, #YMN, 112), date) between -5 and 0 then num_differences else 0 end) as last6month
from ##new_table d
group by emp_no, date
)
select
emp_no
,YMN
,case when last6month = 0 then 5
when last3month = 0 then 4
when thismonth = 0 then 3
when thismonth <= 3 then 2
else 1 end RawScore
from cte_RawScore
ORDER BY day(YMN) desc
drop table ##new_table
I want this the scoring only to be applicable for 6 months from and after July 2017. i.e. the #YMN is a variable that stores the year month number; and the score, according to the above rule applies to the 6 months from 201707.
So 201707 is 1 month,
201708 is 2 months, etc, up to 201712
I wish to have a list of employees with their associated scores, based on the rules mentioned below .
That’s, :
A score of 5 if 0 differences in 6 consecutive months ( from July to December) ;
A score of 4 if 0 differences in 3 consecutive months (from July to December);
A score of 3 if 0 differences for 1 month ( from July to December);
A score of 2 if 1 to 3 differences for 1 month (from July to December);
A score of 1 if 4 or more differences in 1 month (from July to December).
I get the number of differences from a table, but some employees do not appear for certain months; hence I want to give them a difference of 0 if they do not appear for that particular month.
Please assist.

Answer 1

I think I understand what you're getting at. Let me give you a simplified example. You need a table full of dates to join to. In data warehousing we use a Date dimension which has attributes about every date.
For your example your date dimension table could just have Month names or numbers:
1
2
...
12
Let's call this table Months.
Then you would do something like this, to count a zero for months with no data. Here I'm using what's called a Common Table Expression or CTE (the part with the WITH) in place of a table, since I'm not concerned with creating a permanent table right now.
WITH Months AS (
SELECT 1 AS MonthNumber UNION
SELECT 2 UNION
SELECT 3 UNION
SELECT 4 UNION
SELECT 5 UNION
SELECT 6 UNION
SELECT 7 UNION
SELECT 8 UNION
SELECT 9 UNION
SELECT 10 UNION
SELECT 11 UNION
SELECT 12
)
SELECT M.MonthNumber, COUNT(*)
FROM Months as M
LEFT JOIN MyData as D
ON MONTH(D.SomeDateValue) = M.MonthNumber
GROUP BY M.MonthNumber
This will guarantee every month appears with a count, perhaps of zero.