SQL fill next date (month) with loop - sql

Question

I have input table, and need to add missing dates, but not to max, but up to next available month.
so I need to use loop.
SET #mindate = '2021.01'
SET #maxdate = CAST( GETDATE() AS Date ) --date today as max date
while
begin
if #mindate => #maxdate
begin
break
end
set #mindate = #mindate + 1
end
then i can get 1+.. but it does not stop to 7 month
so i totally got stuck with writing loop.
Data table :
could anybody help on code? as most examples are with joins, to data tables, or to one max value.

Answer 1

Paul, I'm assuming that you forgot to specify the month in your mock data.
I hope the code below may help you understand how non-trivial is what you are trying to accomplish :-) Kudos for your will to get rid of loops.
To make it better, I propose a denormalization (CAUTION!):
create another column price_valid_until
the latest prices records will have price_valid_until = '21000101' (aka, far away in the future)
when registering a new price, update the previous with new price_valid_from - 1 day
Here's the solution, with a pretty complex, but efficient query (http://sqlfiddle.com/#!18/4ab23/4)
create table price_history(
SKU varchar(255),
price_valid_from date,
price decimal(16, 2)
)
insert into price_history
values
('a', '20210101', 10),
('a', '20210107', 12),
('b', '20210102', 4),
('b', '20210110', 2),
('b', '20210214', 5);
-- This fiddler won't let me initialize and reference:
--
-- declare
-- #from_date date,
-- #to_date date;
--
-- select
-- #from_date = min(date_from),
-- #to_date = max(date_from)
-- from price_history
with
date_range as(
select
min(price_valid_from) as from_date,
--
eomonth(
max(price_valid_from)
) as to_date
from price_history
),
--
all_dates as(
select from_date as date_in_range
from date_range
-- ----------
union all
-- ----------
select dateadd(day, 1, date_in_range)
from all_dates
where
date_in_range < (
select to_date
from date_range
)
),
--
price_history_boundaries as(
select
ph.SKU,
ph.price,
--
ph.price_valid_from,
-- The latest price, so far, is valid until 01/01/2100
coalesce(
dateadd(
day,
-1,
min(ph_next.price_valid_from)
),
'21000101'
) as price_valid_until
from
price_history ph
left outer join price_history ph_next
on(
ph_next.SKU = ph.SKU
and ph_next.price_valid_from > ph.price_valid_from
)
group by ph.SKU, ph.price_valid_from, ph.price
)
select
phb.SKU,
ad.date_in_range,
phb.price
from
all_dates ad
inner join price_history_boundaries phb
on(
phb.price_valid_from <= ad.date_in_range
and phb.price_valid_until >= ad.date_in_range
)
order by phb.SKU, ad.date_in_range

Answer 2

You can easily achieve your desired result by creating list of dates from which to join to. Here I've used a recursive CTE to create a range of dates, adding 1 month per iteration up to the current date.
It's then a simple matter of joining to your source data, here lead() is handy for limiting the joined rows. Also, assuming SQL Server from the usage of Getdate:
declare #start date=(select Min([date]) from sourcetable);
with m as (
select 1 num, #start [Date]
union all
select num+1 , DateAdd(month,1,m.[date])
from m
where DateAdd(month,1,m.[date]) <= GetDate()
), t as (
select *, Lead([date],1,GetDate()) over (order by [date]) NextDate
from sourcetable
)
select m.[Date], t.sku, t.price
from m
join t on m.[date] >= t.[date] and m.[date] < t.nextdate
See Working Fiddle