Number of Days Between a List of Dates - sql-server

Question

I have a temp table with deals, dates, and volumes in it. What I need is to calculate the days between the effective dates in a dynamic fashion. Also complicating this, the first for each deal is in the past but the represents the current deal volume. So for that line I need to return the number of days from today to the next effective date for that deal. Furthermore, on the last effective date for each deal, I have to run a subquery to grab the contract end date from another temp table.
Sample of the temp table and the sample return needed:
Sample

Answer 1

Here's an option to explore.
Basically what you're after for each record:
Previous record EffectiveDate based on Deal_ID - LAG()
Next EffectiveDate after today based on Deal_ID - Sub query
Then you can evaluate and figure out days based on those values.
Here's a temp table and some sample data:
CREATE TABLE #Deal
(
[Row_ID] INT
, [Deal_ID] BIGINT
, [EffectiveDate] DATE
, [Volume] BIGINT
);
INSERT INTO #Deal (
[Row_ID]
, [Deal_ID]
, [EffectiveDate]
, [Volume]
)
VALUES ( 1, 1479209, '2018-11-01', 5203 )
, ( 2, 1479209, '2019-03-01', 2727 )
, ( 3, 1479209, '2019-04-01', 1615 )
, ( 4, 1479209, '2019-06-01', 1325 )
, ( 5, 1598451, '2018-12-01', 2000 )
, ( 6, 1598451, '2019-04-01', 4000 )
, ( 7, 1598451, '2019-08-01', 4000 );
Here's an example query using LAG() and sub-query:
SELECT *
-- LAG here partitioned by the Deal_ID, will return NULL if first record.
, LAG([dl].[EffectiveDate], 1, NULL) OVER ( PARTITION BY [dl].[Deal_ID]
ORDER BY [dl].[EffectiveDate]
) AS [PreviousRowEffectiveData]
--Sub query to get min EffectiveDate that is greater than today
, (
SELECT MIN([dl1].[EffectiveDate])
FROM #Deal [dl1]
WHERE [dl1].[Deal_ID] = [dl].[Deal_ID]
AND [dl1].[EffectiveDate] > GETDATE()
) AS [NextEffectiveDateAfterToday]
FROM #Deal [dl]
Giving you these results:
Row_ID Deal_ID EffectiveDate Volume PreviousRowEffectiveData NextEffectiveDateAfterToday
----------- -------------------- ------------- -------------------- ------------------------ ---------------------------
1 1479209 2018-11-01 5203 NULL 2019-03-01
2 1479209 2019-03-01 2727 2018-11-01 2019-03-01
3 1479209 2019-04-01 1615 2019-03-01 2019-03-01
4 1479209 2019-06-01 1325 2019-04-01 2019-03-01
5 1598451 2018-12-01 2000 NULL 2019-04-01
6 1598451 2019-04-01 4000 2018-12-01 2019-04-01
7 1598451 2019-08-01 4000 2019-04-01 2019-04-01
Now that we have that we can use that in a sub query and then implement the business rules for DAYS if I understood correctly:
First row for a Deal_ID, number of days from next effective date after today to today.
If not first, number of days from previous effective date to row effective date.
Example query:
SELECT *
--Case statement, if previousrow null(first record) difference in days of datday and NextEfectiveDateAfterToday
--Else we will do the difference in days of previousrow and this rows effective date.
, CASE WHEN [Deal].[PreviousRowEffectiveData] IS NULL THEN DATEDIFF(DAY, GETDATE(), [Deal].[NextEffectiveDateAfterToday])
ELSE DATEDIFF(DAY, [Deal].[PreviousRowEffectiveData], [Deal].[EffectiveDate])
END AS [DAYS]
FROM (
SELECT *
-- LAG here partioned by the Deal_ID, we'l return NULL if first record.
, LAG([dl].[EffectiveDate], 1, NULL) OVER ( PARTITION BY [dl].[Deal_ID]
ORDER BY [dl].[EffectiveDate]
) AS [PreviousRowEffectiveData]
--Sub query to get min EffectiveDate that is greater than today
, (
SELECT MIN([dl1].[EffectiveDate])
FROM #Deal [dl1]
WHERE [dl1].[Deal_ID] = [dl].[Deal_ID]
AND [dl1].[EffectiveDate] > GETDATE()
) AS [NextEffectiveDateAfterToday]
FROM #Deal [dl]
) AS [Deal];
Giving us the final results of:
Row_ID Deal_ID EffectiveDate Volume PreviousRowEffectiveData NextEffectiveDateAfterToday DAYS
----------- -------------------- ------------- -------------------- ------------------------ --------------------------- -----------
1 1479209 2018-11-01 5203 NULL 2019-03-01 14
2 1479209 2019-03-01 2727 2018-11-01 2019-03-01 120
3 1479209 2019-04-01 1615 2019-03-01 2019-03-01 31
4 1479209 2019-06-01 1325 2019-04-01 2019-03-01 61
5 1598451 2018-12-01 2000 NULL 2019-04-01 45
6 1598451 2019-04-01 4000 2018-12-01 2019-04-01 121
7 1598451 2019-08-01 4000 2019-04-01 2019-04-01 122