Dynamic 12 month rolling total for each previous month, going back 12 months - sql

Question

I have the following sql Code (where clause just to limit rows currently)
select
month,
monthname,
year,
count(distinct case when a.dim_service_type_id_desc like '%Direct Payment%' then a.DIM_PERSON_ID else null end) as No_dp,
count(distinct a.DIM_PERSON_ID) as no_ppl
from
SERVICE_PROVISIONS a
inner join date_tbl d on CONVERT(VARCHAR(35),a.start_dttm,112) = d.dim_date_id
where
a.dim_person_id >0
and year = 2018
group by
month,
monthname,
year
my output is this
month monthname year No_dp no_ppl
1 January 2018 142 1604
2 February 2018 111 1526
3 March 2018 133 1636
4 April 2018 1107 3829
5 May 2018 140 1575
6 June 2018 131 1389
7 July 2018 200 893
8 August 2018 2 73
9 September 2018 1 32
10 October 2018 2 21
11 November 2018 2 21
12 December 2018 2 19
So my question is - the customer wants to see how many services were open (using start date and end date) during the previous 12 months (not how many were started, but how many were current and not ended). This is fine when using the current month, however they want to show this also for the previous 12 months as a rolling dynamic figure.
So for example this month in July they want to see how many services were open during the last 12 months. Last month June, they want to see how many services were open during the 12 months previous to June and so on for the previous 12 months.
The table needs to have the month name for the last 12 months and in a column show the number of services that were open in the previous 12 months next to that month.
I hope that makes sense, sorry if it doesn't, feel free to ask questions and I will try to clarify.
The output needs to look something like the current output table, but it is currently only showing how many services were started within that month, which isn't what we want.
The date table is a reference table which has different date formats etc. It can be used or added to if needed.

Answer 1

I've had to make several assumptions about your data. Hopefully the query I'll show in a minute will be easy for you to adjust if any of these are wrong:
I am guessing by its name that start_dttm is a datetime or datetime2 column.
I assume there is a corresponding column called end_dttm that gives the end date/time of a service, and that a null in this column would indicate that a service has not yet ended.
My best guess as to what it means for a service to be "open" in a given month is that it began sometime either within or prior to that month, and has not ended by the time that month is over.
I assume from your original query that multiple services having the same dim_person_id do not represent distinct services.
Since I don't know what's in your date_tbl, I'll show an example that doesn't require it. Consider the following query:
select
BeginDate = dateadd(month, -1, dateadd(day, 1, eomonth(getdate(), -Offset.X))),
EndDate = dateadd(day, 1, eomonth(getdate(), -Offset.X))
from
(values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11)) Offset(X)
This will give you 12 records, representing the current month and each of the 11 preceding months. Note that my EndDate here is not actually the last day of the month, but the first day of the following month. I've done this because of assumption 1 above; since your service dates may have time components, I'll determine whether they fall in a given month by checking if their dates are strictly earlier than the start of the following month. Here's what that query gives me:
BeginDate EndDate
2018-07-01 2018-08-01
2018-06-01 2018-07-01
2018-05-01 2018-06-01
2018-04-01 2018-05-01
2018-03-01 2018-04-01
2018-02-01 2018-03-01
2018-01-01 2018-02-01
2017-12-01 2018-01-01
2017-11-01 2017-12-01
2017-10-01 2017-11-01
2017-09-01 2017-10-01
2017-08-01 2017-09-01
Now I'll join the above result set to your SERVICE_PROVISIONS data, looking for records in each month that have dim_person_id > 0 (from your original query) and which satisfy assumption 3 above.
-- Some sample data (assumptions 1 & 2)
declare #SERVICE_PROVISIONS table (dim_person_id bigint, start_dttm datetime, end_dttm datetime);
insert #SERVICE_PROVISIONS values
(1, '20180101', '20180315'),
(1, '20180101', '20180315'),
(2, '20171215', '20180520');
-- The CTE defines the months we'll report on, as described earlier.
with MonthsCTE as
(
select
BeginDate = dateadd(month, -1, dateadd(day, 1, eomonth(getdate(), -Offset.X))),
EndDate = dateadd(day, 1, eomonth(getdate(), -Offset.X))
from
(values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11)) Offset(X)
)
-- This query matches the months from the CTE against the applicable services.
select
[Month] = datepart(month, M.BeginDate),
[MonthName] = datename(month, M.BeginDate),
[Year] = datepart(year, M.BeginDate),
ServicesOpen = count(distinct S.dim_person_id) -- Assumption 4
from
MonthsCTE M
left join #SERVICE_PROVISIONS S on
S.dim_person_id > 0 and
S.start_dttm < M.EndDate and -- Assumption 3
(
S.end_dttm >= M.EndDate or
S.end_dttm is null -- Assumption 2
)
group by
M.BeginDate,
M.EndDate
order by
M.BeginDate;
Note that I moved the dim_person_id > 0 from the WHERE clause to the JOIN so that each of the 12 months will still appear in the result set even if there were no services open during that time. Results:
Month MonthName Year ServicesOpen
8 August 2017 0
9 September 2017 0
10 October 2017 0
11 November 2017 0
12 December 2017 1
1 January 2018 2
2 February 2018 2
3 March 2018 1
4 April 2018 1
5 May 2018 0
6 June 2018 0
7 July 2018 0

Answer 2

something a bit like this - if you can write a query to get the value you want for a row in your ootput, then use cross apply to link to that query. Counting records that have an open record before the month, but no close record before the month seems feasible
SELECT IQ. *, OA.SERVICE_PROVISIONS FROM (select
month,
monthname,
year,
a.dim_person_id dim_person_id,
count(distinct case when a.dim_service_type_id_desc like '%Direct Payment%' then a.DIM_PERSON_ID else null end) as No_dp,
count(distinct a.DIM_PERSON_ID) as no_ppl
from
SERVICE_PROVISIONS a
inner join date_tbl d on CONVERT(VARCHAR(35),a.start_dttm,112) = d.dim_date_id
where
a.dim_person_id >0
and year = 2018
group by
month,
monthname,
year) IQ
CROSS APPLY
(SELECT count(0) OpenThings FROM SERVICE_PROVISIONS SP1 WHERE
(sp1.startdate < DATEFROMPARTS(IQ.year,iq.month,1)
AND
sp1.enddate is null or sp1.enddate > DATEFROMPARTS(IQ.year,iq.month,1)) and sp1.dim_person_id = iq.dim_person_id
) AS OA