SQL Summary of Status total values by Month of Type2 SC Dimension - sql

Question

I have a voucher status history table as a type2 slowly changing dimension table I am trying to get the summary total value of each status by each month before a particular date. This is my schema and insert code:
CREATE TABLE #HDimVouchers(
[HVoucherKey] [bigint] IDENTITY(1,1) NOT NULL,
[Voucher_id] [bigint] NOT NULL,
[VoucherStatusKey] [int] NOT NULL,
[Voucher_amt] [decimal](18, 2) NULL,
[DateStatusStart] [date] NULL,
[DateStatusEnd] [date] NULL
)
--drop table #HDimVouchers
insert #HDimVouchers
values
(10,2,10.00,'2019-01-01','2019-02-15'),
(10,4,10.00,'2019-02-16',null),
(13,4,10.00,'2019-01-10',null),
(11,2,15.00,'2019-01-01',null),
(12,2,20.00,'2019-03-12','2019-03-12'),
(12,4,20.00,'2019-03-13',null),
(15,2,205.00,'2019-05-25','2020-04-24'),
(15,6,205.00,'2020-04-25',null),
(21,2,100.00,'2019-02-16',null)
I would like to get a summary to total value by year-month by voucherstatuskey something like the below:
[Year-Month]
[VoucherStatusKey]
[Amount]
201901
2
25
201901
4
10
201902
2
100
201902
4
10
201903
4
20
201905
2
205
201906
2
205
201907
2
205
201908
2
205
201909
2
205
201910
2
205
201911
2
205
201912
2
205
202001
2
205
202002
2
205
202003
2
205
I have had many attempts to get the data as above, but I am struggling to get the correct format and values. Below is something I have tried
SELECT convert(nvarchar(4),Year([DateStatusStart])) + RIGHT('00' + CONVERT(NVARCHAR(2), DATEPART(Month, [DateStatusStart])), 2)
,[VoucherStatusKey]
,SUM([Voucher_amt]) OVER (PARTITION BY Year([DateStatusStart]),Month([DateStatusStart]), [VoucherStatusKey] ORDER BY [DateStatusStart]) AS running_total
FROM #HDimVouchers where [DateStatusStart] < '2020-03-31';

Answer 1

Let me assume that you want the value at the end of the month. Then, you can take the following approach:
Generate all appropriate months for each voucher.
Use a join to bring in the appropriate value.
For the first part, you could use a tally or calendar table if one is available. However a recursive CTE is also convenient:
with vdates as (
select voucher_id, eomonth(min(DateStatusStart)) as eom
from HDimVouchers
group by voucher_id
union all
select voucher_id, eomonth(dateadd(month, 1, eom))
from vdates
where eom < '2020-03-01'
)
select vd.*, hv.Voucher_amt
from vdates vd join
HDimVouchers hv
on hv.voucher_id = vd.voucher_id and
vd.eom >= hv.DateStatusStart and
(vd.eom <= hv.DateStatusEnd or hv.DateStatusEnd is null)
order by vd.eom, vd.voucher_id;
Here is a db<>fiddle.

Answer 2

My take on this would be:
;with [dates] as (
select YEAR(MIN([DateStatusStart]))*100+MONTH(MIN([DateStatusStart])) [YM] from #HDimVouchers
union all
select case when ([dates].[YM] % 100) = 12 then [dates].[YM] + 100 - 11 else [dates].[YM] + 1 end from [dates] where [YM] < 202112
), [dimkeys] as (
select
[Voucher_id],
YEAR(MIN([DateStatusStart]))*100+MONTH(MIN([DateStatusStart])) [DateStatusStart],
YEAR(MAX(ISNULL([DateStatusEnd], DATEFROMPARTS(2999, 12, 31))))*100+MONTH(MAX(ISNULL([DateStatusEnd], DATEFROMPARTS(2999, 12, 31)))) [DateStatusEnd]
from [#HDimVouchers] group by [Voucher_id]
), [map] as (
select
[dimkeys].[Voucher_id],
[dates].[YM],
COALESCE(
MAX([d].[DateStatusStart]),
(select MAX([i].[DateStatusStart]) from [#HDimVouchers] [i] where [i].[Voucher_id] = [dimkeys].[Voucher_id] and YEAR([i].[DateStatusStart])*100+MONTH([i].[DateStatusStart]) < [dates].[YM]),
(select MIN([i].[DateStatusStart]) from [#HDimVouchers] [i] where [i].[Voucher_id] = [dimkeys].[Voucher_id])
) [MappingDate]
from [dates]
cross join [dimkeys]
left join [#HDimVouchers] [d] on [d].[Voucher_id] = [dimkeys].[Voucher_id] and YEAR([d].[DateStatusStart])*100+MONTH([d].[DateStatusStart]) = [dates].[YM]
where [dates].[YM] >= [dimkeys].[DateStatusStart] and [dates].[YM] <= [dimkeys].[DateStatusEnd]
group by [dimkeys].[Voucher_id], [dates].[YM]
)
select [map].[YM], [fact].[VoucherStatusKey], SUM([fact].[Voucher_amt]) [Sum]
from [map] join [#HDimVouchers] [fact] on [fact].[Voucher_id] = [map].[Voucher_id] and [fact].[DateStatusStart] = [map].[MappingDate]
group by [map].[YM], [fact].[VoucherStatusKey]
order by [YM], [VoucherStatusKey];
So:
Get all year-month values from start to end
Get all distinct keys with their overall min/max dates (aka when the member exists)
cross join them to get an entry of every key for every yearmonth (within lifetime of member)
add the date which should be used for mapping (this is used to decide to which month to add a member that was changed in a year-month)
only then join this up with the full dimension and group by the SCD Type 2 attribute
Update
For big tables, you can split it up in multiple temp. tables instead of going all out on CTEs. That usually helps a lot on performance.
select *,
YEAR([DateStatusStart])*100+MONTH([DateStatusStart]) [YmStart],
YEAR([DateStatusEnd])*100+MONTH([DateStatusEnd]) [YmEnd]
into [#withYm]
from [#HDimVouchers];
;with [dates] as (
select MIN([YmStart]) [YM] from [#withYm]
union all
select case when ([dates].[YM] % 100) = 12 then [dates].[YM] + 100 - 11 else [dates].[YM] + 1 end from [dates] where [YM] < 202112
), [dimkeys] as (
select
[Voucher_id],
MIN([YmStart]) [YmStart],
MAX(ISNULL([YmEnd], 299912)) [YmEnd]
from [#withYm]
group by [Voucher_id]
)
select
[dimkeys].[Voucher_id],
[dates].[YM]
into [#all]
from [dates]
cross join [dimkeys]
where [dates].[YM] >= [dimkeys].[YmStart] and [dates].[YM] <= [dimkeys].[YmEnd]
;with [map] as (
select
[#all].[Voucher_id],
[#all].[YM],
ISNULL(
MAX([d].[DateStatusStart]),
(select MAX([i].[DateStatusStart]) from [#withYm] [i] where [i].[Voucher_id] = [#all].[Voucher_id] and [i].[YmStart] < [#all].[YM])
) [MappingDate]
from [#all]
left join [#HDimVouchers] [d] on [d].[Voucher_id] = [#all].[Voucher_id] and YEAR([d].[DateStatusStart])*100+MONTH([d].[DateStatusStart]) = [#all].[YM]
group by [#all].[Voucher_id], [#all].[YM]
)
select [map].[YM], [fact].[VoucherStatusKey], SUM([fact].[Voucher_amt]) [Sum]
from [map] join [#HDimVouchers] [fact] on [fact].[Voucher_id] = [map].[Voucher_id] and [fact].[DateStatusStart] = [map].[MappingDate]
group by [map].[YM], [fact].[VoucherStatusKey]
order by [YM], [VoucherStatusKey];