Looking up the first row of results - sql-server

Question

I have a history table containing a snapshot of each time a record is changed. I'm trying to return a certain history row with the original captured date. I am currently using this at the moment:
select
s.Description,
h.CaptureDate OriginalCaptureDate
from
HistoryStock s
left join
( select
StockId,
CaptureDate
from
HistoryStock
where
HistoryStockId in ( select MIN(HistoryStockId) from HistoryStock group by StockId )
) h on s.StockId = h.StockId
where
s.HistoryStockId = #HistoryStockId
This works but with 1 Million records its on the slow side and I'm not sure how to optimize this query.
How can this query be optimized?
UPDATE:
WITH OriginalStock (StockId, HistoryStockId)
AS (
SELECT StockId, min(HistoryStockId)
from HistoryStock group by StockId
),
OriginalCaptureDate (StockId, OriginalCaptureDate)
As (
SELECT h.StockId, h.CaptureDate
from HistoryStock h join OriginalStock o on h.HistoryStockId = o.HistoryStockId
)
select
s.Description,
h.OriginalCaptureDate
from
HistoryStock s left join OriginalCaptureDate h on s.StockId = h.StockId
where
s.HistoryStockId = #HistoryStockId
I've update the code to use CTE but I'm not better off performance wise, only have small performance increase. Any ideas?
Just another note, I need to get to the first record in the history table for StockId and not the earliest Capture date.

Answer 1

I am not certain I understand entirely how the data works from your query but nesting queries like that is never good for performance in my opinion. You could try something along the lines of:
WITH MinCaptureDate (StockID, MinCaptureDate)
AS (
SELECT HS.StockID
,MIN(HS.CaptureDate) AS OriginalCaptureDate
FROM HistoryStock HS
GROUP BY
HS.Description
)
SELECT HS.Description
,MCD.OriginalCaptureDate
FROM HistoryStock HS
JOIN MinCaptureDate MCD
ON HS.StockID = MCD.StockID
WHERE HS.StockID = #StockID

Answer 2

I think i see what you are trying to achieve. You basically want the description of the specified history stock record, but you want the date associated with the first history record for the stock... so if your history table looks like this
StockId HistoryStockId CaptureDate Description
1 1 Apr 1 Desc 1
1 2 Apr 2 Desc 2
1 3 Apr 3 Desc 3
and you specify #HistoryStockId = 2, you want the following result
Description OriginalCaptureDate
Desc 2 Apr 1
I think the following query would give you a slightly better performance.
WITH OriginalStock (StockId, CaptureDate, RowNumber)
AS (
SELECT
StockId,
CaptureDate,
RowNumber = ROW_NUMBER() OVER (PARTITION BY StockId ORDER BY HistoryStockId ASC)
from HistoryStock
)
select
s.Description,
h.CaptureDate
from
HistoryStock s left join OriginalStock h on s.StockId = h.StockId and h.RowNumber = 1
where
s.HistoryStockId = #HistoryStockId