Insert missing records for each month/year with the previous month's value

Question

Insert missing records for each month/year with the previous month's value

sxzhu

SSC Enthusiast

Points: 178
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July 28, 2020 at 3:34 am

#3775263

I have a sample data, see below.
Sample data
The base rules are
If the same CustomerID and Account# for the month that don't exist based on the previous month, then insert it;
If the same CustomerID and Account# for the month that do exist based on the previous month, then keep it.
For example, a record of the CustomerID 14 has not been updated since Dec. 2019. We need to add it into the missing months. The CustomerID 20 for Account# 1 also missed three records in Jan., Feb. and Apr. 2020. The output should look like this, see Expected results.
Expected results
Is there a Fastest way to do it since we have over 20 Million records and the date of the data starts from 2014?
Thank you very much.

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Steve Collins SSCrazy Points: 2072 More actions · Answer 1

drop table if exists dbo.#TestDates;
go
create table dbo.#TestDates(
  yr        int not null,
  mo        int not null,
  cust_id   int not null,
  acct_num  int not null,
  amnt      int not null);
go

drop table if exists dbo.#TestDates_fixed;
go
create table dbo.#TestDates_fixed(
  yr        int not null,
  mo        int not null,
  cust_id   int not null,
  acct_num  int not null,
  amnt      int not null,
  row_src   char(3));
go

insert #TestDates(yr, mo, cust_id, acct_num, amnt) values
(2019, 11, 14, 1, 200),
(2019, 11, 20, 1, 500),
(2019, 11, 20, 2,  25),
(2019, 12, 20, 1, 670),
(2019, 12, 20, 2,  50),
(2020,  1, 20, 2, 700),
(2020,  2, 20, 2, 746),
(2020,  3, 20, 1, 550),
(2020,  3, 20, 2, 600),
(2020,  4, 20, 2, 720);

declare
  @end_dt         date='2020-04-01';

;with dt_range_cte(cust_id, acct_num, mo_dt, lead_dt, lead_diff, amnt) as (
    select
      td.cust_id,
      td.acct_num,
      m.mo_dt,
      lead(m.mo_dt) over (partition by td.cust_id, td.acct_num order by m.mo_dt),
      datediff(month, m.mo_dt, isnull(lead(m.mo_dt) over (partition by td.cust_id, td.acct_num order by m.mo_dt), @end_dt)),
      td.amnt
    from 
      #TestDates td
     cross apply
      (select datefromparts(td.yr, td.mo, 1) mo_dt) m)
insert #TestDates_fixed(yr, mo, cust_id, acct_num, amnt, row_src)
select *, 'old' from #TestDates
union all
select
  year(da.nxt_mo), month(da.nxt_mo), drc.cust_id, drc.acct_num, drc.amnt, 'new'
from
  dt_range_cte drc
 cross apply
  dbo.fnTally(0, drc.lead_diff) f
 cross apply
  (select dateadd(month, f.n, drc.mo_dt) nxt_mo) da
where
  f.n>0
  and (drc.lead_dt is null or (drc.lead_dt is not null and f.n<>drc.lead_diff));

select * from #TestDates_fixed tdf order by 3, 4, 1, 2;