How to Determine Values for Missing Months based on Data of Previous Months in T-SQL

Question

I have a set of transactions occurring at specific points in time:

CREATE TABLE Transactions (
    TransactionDate Date NOT NULL,
    TransactionValue Intege         


        

Answer 1

John Gibb posted a fine answer, already accepted, but I wanted to expand on it a bit to:

• eliminate the one year limitation,
• expose the date range in a more explicit manner, and
• eliminate the need for a separate numbers table.

This slight variation uses a recursive common table expression to establish the set of Dates representing the first of each month on or after from and to dates defined in DateRange. Note the use of the MAXRECURSION option to prevent a stack overflow (!); adjust as necessary to accommodate the maximum number of months expected. Also, consider adding alternative Dates assembly logic to support weeks, quarters, even day-to-day.

with 
DateRange(FromDate, ToDate) as (
  select 
    Cast('11/1/2008' as DateTime), 
    Cast('2/15/2010' as DateTime)
),
Dates(Date) as (
  select 
    Case Day(FromDate) 
      When 1 Then FromDate
      Else DateAdd(month, 1, DateAdd(month, ((Year(FromDate)-1900)*12)+Month(FromDate)-1, 0))
    End
  from DateRange
  union all
  select DateAdd(month, 1, Date)
  from Dates
  where Date < (select ToDate from DateRange)
)
select 
  d.Date, t.TransactionValue
from Dates d
outer apply (
  select top 1 TransactionValue
  from Transactions
  where TransactionDate <= d.Date
  order by TransactionDate desc
) t
option (maxrecursion 120);