An Ugly Self-join (oh, That Doesn't Work!!)

Hi again, all...here I am again, trying to work on my CloseIndex thang again...Same subject, different tack...

Basically, I have two tables...for the sake of simplicity, let me define them as:


PortfolioIndex
PortfolioID int
CreateDate smalldatetime
CloseIndex float

PortfolioPerformance
PortfolioID int
CreateDate smalldatetime
PrevDate smalldatetime
DailyPerChg float

UPDATE PortfolioIndex
SET CloseIndex = CASE
WHEN PPI.CloseIndex IS NULL THEN 100.00
ELSE (PPI.CloseIndex + (PPI.CloseIndex * PP.DailyPerChg / 100))
END
FROM PortfolioIndex AS P INNER JOIN PortfolioIndex AS PPI on (P.PortfolioID = PPI.PortfolioID), PortfolioPerformance AS PP
WHERE (P.PortfolioID = PP.PortfolioID) AND
((P.CreateDate = PP.CreateDate) AND
(P.CreateDate = @CreateDate) AND
(PPI.CreateDate = PP.PrevDate))


What I am trying to do is...get the previous day's portfolioIndex row's CloseIndex and create a new one for today's row.

As ugly as it is, it works when I execute it in the SQL Query Analyzer, but when I try to create the stored procedure, the syntax check complains that the PortfolioIndex reference at the UPDATE... part is AMBIGUOUS...yet when I define it in the SP as P.PortfolioIndex, it fails at run time saying there is no object named P.PortfolioIndex (well, of course there isn't!).

How can I make this work (and if possible, make it prettier too! *L* ;) )