TSQL Get Item Price History from Item Price Changes - tsql

Question

I have a table of item price changes, and I want to use it to create a table of item prices for each date (between the item's launch and end dates).
Here's some code to create the date:-
declare #Item table (item_id int, item_launch_date date, item_end_date date);
insert into #Item Values (1,'2001-01-01','2016-01-01'), (2,'2001-01-01','2016-01-01')
declare #ItemPriceChanges table (item_id int, item_price money, my_date date);
INSERT INTO #ItemPriceChanges VALUES (1, 123.45, '2001-01-01'), (1, 345.34, '2001-01-03'), (2, 34.34, '2001-01-01'), (2,23.56 , '2005-01-01'), (2, 56.45, '2016-05-01'), (2, 45.45, '2017-05-01'); ;
What I'd like to see is something like this:-
item_id date price
------- ---- -----
1 2001-01-01 123.45
1 2001-01-02 123.45
1 2001-01-03 345.34
1 2001-01-04 345.34
etc.
2 2001-01-01 34.34
2 2001-01-02 34.34
etc.
Any suggestions on how to write the query?
I'm using SQL Server 2016.
Added:
I also have a calendar table called "dim_calendar" with one row per day. I had hoped to use a windowing function, but the nearest I can find is lead() and it doesn't do what I thought it would do:-
select
i.item_id,
c.day_date,
ipc.item_price as item_price_change,
lead(item_price,1,NULL) over (partition by i.item_id ORDER BY c.day_date) as item_price
from dim_calendar c
inner join #Item i
on c.day_date between i.item_launch_date and i.item_end_date
left join #ItemPriceChanges ipc
on i.item_id=ipc.item_id
and ipc.my_date=c.day_date
order by
i.item_id,
c.day_date;
Thanks

Answer 1

I wrote this prior to your edit. Note that your sample output suggests that an item can have two prices on the day of the price change. The following assumes that an item can only have one price on a price change day and that is the new price.
declare #Item table (item_id int, item_launch_date date, item_end_date date);
insert into #Item Values (1,'2001-01-01','2016-01-01'), (2,'2001-01-01','2016-01-01')
declare #ItemPriceChange table (item_id int, item_price money, my_date date);
INSERT INTO #ItemPriceChange VALUES (1, 123.45, '2001-01-01'), (1, 345.34, '2001-01-03'), (2, 34.34, '2001-01-01'), (2,23.56 , '2005-01-01'), (2, 56.45, '2016-05-01'), (2, 45.45, '2017-05-01');
SELECT * FROM #ItemPriceChange
-- We need a table variable holding all possible date points for the output
DECLARE #DatePointList table (DatePoint date);
DECLARE #StartDatePoint date = '01-Jan-2001';
DECLARE #MaxDatePoint date = GETDATE();
DECLARE #DatePoint date = #StartDatePoint;
WHILE #DatePoint <= #MaxDatePoint BEGIN
INSERT INTO #DatePointList (DatePoint)
SELECT #DatePoint;
SET #DatePoint = DATEADD(DAY,1,#DatePoint);
END;
-- We can use a CTE to sequence the price changes
WITH ItemPriceChange AS (
SELECT item_id, item_price, my_date, ROW_NUMBER () OVER (PARTITION BY Item_id ORDER BY my_date ASC) AS SeqNo
FROM #ItemPriceChange
)
-- With the price changes sequenced, we can derive from and to dates for each price and use a join to the table of date points to produce the output. Also, use an inner join back to #item to only return rows for dates that are within the start/end date of the item
SELECT ItemPriceDate.item_id, DatePointList.DatePoint, ItemPriceDate.item_price
FROM #DatePointList AS DatePointList
INNER JOIN (
SELECT ItemPriceChange.item_id, ItemPriceChange.item_price, ItemPriceChange.my_date AS from_date, ISNULL(ItemPriceChange_Next.my_date,#MaxDatePoint) AS to_date
FROM ItemPriceChange
LEFT OUTER JOIN ItemPriceChange AS ItemPriceChange_Next ON ItemPriceChange_Next.item_id = ItemPriceChange.item_id AND ItemPriceChange.SeqNo = ItemPriceChange_Next.SeqNo - 1
) AS ItemPriceDate ON DatePointList.DatePoint >= ItemPriceDate.from_date AND DatePointList.DatePoint < ItemPriceDate.to_date
INNER JOIN #item AS item ON item.item_id = ItemPriceDate.item_id AND DatePointList.DatePoint BETWEEN item.item_launch_date AND item.item_end_date
ORDER BY ItemPriceDate.item_id, DatePointList.DatePoint;

Answer 2

#AlphaStarOne Perfect! I've modified it to use a Windowing function rather than a self-join, but what you've suggested works. Here's my implementation of that in case anyone else needs it:
SELECT
ipd.item_id,
dc.day_date,
ipd.item_price
FROM dim_calendar dc
INNER JOIN (
SELECT
item_id,
item_price,
my_date AS from_date,
isnull(lead(my_date,1,NULL) over (partition by item_id ORDER BY my_date),getdate()) as to_date
FROM #ItemPriceChange ipc1
) AS ipd
ON dc.day_date >= ipd.from_date
AND dc.day_date < ipd.to_date
INNER JOIN #item AS i
ON i.item_id = ipd.item_id
AND dc.day_date BETWEEN i.item_launch_date AND i.item_end_date
ORDER BY
ipd.item_id,
dc.day_date;