Question : SQL Select statement question

I need to return a date, a Price and a Price from the previous date in a select statement. I am not sure how to do this.

I have a table that contains 3 fields
NodeDate, daPrice,rtPrice

NodeDate  is a SmallDateTime
daPrice is a Decimal(9,4)
rtPrice is a Decimal(9,4)

e.g.
NodeDate     daPrice      rtPrice
7/29/2010       2.3             2.4
7/28/2010       5                5.8
7/27/2010      2.5               0.4

I need to return NodeDate, (daPrice - rtPrice) as TodayDifference, (daPric-rtPrice this is YESTERDAY's data) as DifferenceFromYesterday

I think I could do this with something like
Select NodeDate, (daPrice-rtPrice) as TodayDifference, (Select Y.daPrice -Y.rtPrice From Table Y where Dateadd('d',-1,T.NodeDate) = Y.NodeDate) As DifferenceFromYesterday
From Table T

However, I do not think this is a very efficient method. There are close to 200,000,000 records that will be processed and I only want the Top 40 to be returned. Even if I add the TOP clause to the SQL statement, I am concerned that my version will take a long time to execute.

Does anyone have a suggestion?
thanks,
pat

Answer : SQL Select statement question

Update:  I just found the following article:
Finally, I found the answer to the problem. This hint sent me in the right direction. Even though the Welcome Screen and Fast User switching were OFF/DISABLED the all important registry key had not been changed. The following key was still set to "1" when I changed it to "0" offline files stopped unchecking itself after every reboot.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
"AllowMultipleTSSessions"=dword:00000000

This laptop had the setting to 1.  Going into User accounts in Control panel to look at the enable/disable setting produces a message stating that tvt_gina.dll has turned off welcome screen and fast user switching.  That belongs to Thinkvantage line of software.  Only this computer has the updated versions of software.

This resolved my issue.