lironavr February 2016

Populating a list of dates without a defined end date - SQL server

I have a list of accounts and their cost which changes every few days. In this list I only have the start date every time the cost updates to a new one, but no column for the end date. Meaning, I need to populate a list of dates when the end date for a specific account and cost, should be deduced as the start date of the same account with a new cost.

More or less like that:
Account   start date  cost
 one           1/1/2016   100$
 two           1/1/2016   150$
 one           4/1/2016   200$
 two           3/1/2016   200$

And the result I need would be:
Account    date    cost
 one       1/1/2016  100$
 one       2/1/2016  100$
 one       3/1/2016  100$
 one       4/1/2016  200$
 two       1/1/2016  150$
 two       2/1/2016  150$
 two       3/1/2016  200$

For example, if the cost changed in the middle of the month, than the sample data will only hold two records (one per each unique combination of account-start date-cost), while the results will hold 30 records with the cost for each and every day of the month (15 for the first cost and 15 for the second one). The costs are a given, and no need to calculate them (inserted manually).

Note the result contains more records because the sample data shows only a start dat

Answers


t-clausen.dk February 2016

Solution is a bit long.

I added an extra date for test purposes:

DECLARE @t table(account varchar(10), startdate date, cost int)

INSERT @t 
values
('one','1/1/2016',100),('two','1/1/2016',150),
('one','1/4/2016',200),('two','1/3/2016',200),
('two','1/6/2016',500) -- extra row

;WITH CTE as
( SELECT
    row_number() over (partition by account order by startdate) rn,
    *
  FROM @t
),N(N)AS 
(
  SELECT 1 FROM(VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))M(N)
),
tally(N) AS -- tally is limited to 1000 days
(
  SELECT ROW_NUMBER()OVER(ORDER BY N.N) - 1 FROM N,N a,N b
),GROUPED as
(
  SELECT
    cte.account, cte.startdate, cte.cost, cte2.cost cost2, cte2.startdate enddate
  FROM CTE
  JOIN CTE CTE2
  ON CTE.account = CTE2.account
  and CTE.rn = CTE2.rn - 1
)
-- used DISTINCT to avoid overlapping dates
SELECT DISTINCT
  CASE WHEN datediff(d, startdate,enddate) = N THEN cost2 ELSE cost END cost,
  dateadd(d, N, startdate) startdate,
  account
FROM grouped
JOIN tally
ON datediff(d, startdate,enddate) >= N

Result:

cost  startdate   account
100   2016-01-01  one
100   2016-01-02  one
100   2016-01-03  one
150   2016-01-01  two
150   2016-01-02  two
200   2016-01-03  two
200   2016-01-04  one
200   2016-01-04  two
200   2016-01-05  two
500   2016-01-06  two


lironavr February 2016

Thank you @t-clausen.dk!

It didn't solve the problem completely, but did direct me in the correct way.

Eventually I used the LEAD function to generate an end date for every cost per account, and then I was able to populate a list of dates based on that idea.

Here's how I generate the end dates:

DECLARE @t table(account varchar(10), startdate date, cost int)
INSERT @t 
values
('one','1/1/2016',100),('two','1/1/2016',150),
('one','1/4/2016',200),('two','1/3/2016',200),
('two','1/6/2016',500)

select account 
      ,[startdate]
      ,DATEADD(DAY, -1, LEAD([Startdate], 1,'2100-01-01') OVER (PARTITION BY account ORDER BY [Startdate] ASC)) AS enddate 
      ,cost
from @t

It returned the expected result:

account   startdate        enddate       cost
  one       2016-01-01    2016-01-03      100
  one       2016-01-04    2099-12-31      200
  two       2016-01-01    2016-01-02      150
  two       2016-01-03    2016-01-05      200
  two       2016-01-06    2099-12-31      500

Please note that I set the end date of current costs to be some date in the far future which means (for me) that they are currently active.

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Asked in February 2016
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