SQL Server - How to fill in missing column values - sql

Question

I have set of records at day level with 2 columns:
Invoice_date
Invoice_amount
For few records, value of invoice_amount is missing.
I need to fill invoice_amount values where it is NULL using this logic:
Look for next available invoice_amount (in dates later than the blank value record date)
For records with invoice_amount still blank (invoice_amount not present for future dates), look for most previous invoice_amount (in dates before the blank value date)
Note: We have consecutive multiple days where invoice_amount is blank in the dataset:

Answer 1

use CROSS APPLY to find next and previous not null Invoice Amount
update p
set Invoice_Amount = coalesce(nx.Invoice_Amount, pr.Invoice_Amount)
from Problem p
outer apply -- Next non null value
(
select top 1 *
from Problem x
where x.Invoice_Amount is not null
and x.Invoice_Date > p.Invoice_Date
order by Invoice_Date
) nx
outer apply -- Prev non null value
(
select top 1 *
from Problem x
where x.Invoice_Amount is not null
and x.Invoice_Date < p.Invoice_Date
order by Invoice_Date desc
) pr
where p.Invoice_Amount is null
this updates back your table. If you need a select query, it can be modify to it easily

Answer 2

Not efficient but seems to work. Try:
update test set invoice_amount =
coalesce ((select top 1 next.invoice_amount from test next
where next.invoiceDate > test.invoiceDate and next.invoice_amount is not null
order by next.invoiceDate),
(select top 1 prev.invoice_amount from test prev
where prev.invoiceDate < test.invoiceDate and prev.invoice_amount is not null
order by prev.invoiceDate desc))
where invoice_amount is null;

Answer 3

As per given example you could use window function with self join
update t set t.amount = tt.NewAmount
from table t
inner join (
select Dates, coalesce(min(amount) over (order by dates desc ROWS BETWEEN 1 PRECEDING AND CURRENT ROW),
min(amount) over (order by dates asc ROWS BETWEEN 1 PRECEDING AND CURRENT ROW)) NewAmount
from table t
) tt on tt.dates = t.dates
where t.amount is null