SQL query Optimization help

I have the the following SQL query

Declare @tempcalctbl Table
(
    ItemId varchar(50),
    ItemLocation varchar(50),
    ItemNo varchar(50),
    Width real,
    Unit varchar(50),
    date datetime
)

Insert Into @tempcalctbl 
     Select distinct SubId,ItemLocation,ItemNo,
       (ABS((Select width From @temptbl a Where ItemProcess ='P1'and a.ItemId = c.ItemId 
           and a.ItemNo = c.ItemNo and a.ItemLocation = c.ItemLocation)
       -(Select width From @temptbl b Where ItemP开发者_运维技巧rocess ='P2' and b.ItemId = c.ItemId 
           and b.ItemNo = c.ItemNo and b.ItemLocation = c.ItemLocation))) * 1000,
       Unit,date
From @temptbl c
Group by ItemId,ItemLocation,ItemNo,Unit,date

I was wondering how to optimize this query. The idea is to find out the different in width (p1's item - p2's item) between ItemProcess 'P1' and 'P2' according to the same ItemID, same ItemNo and same ItemLocation. I have around 75000 and it took more then 25 minute to get the width differences for all the ItemId.

I tried to use Group by for the width different calculation but it would return multiple row instead of just a value which then would return error. By the way I am use MS SQL server 2008 and @tempcalctbl is a table that I declared in a store procedure.

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Does the following help?

INSERT  INTO @tempcalctbl
SELECT  P1.SubId ,
        P1.ItemLocation ,
        P1.ItemNo ,
        ABS(P1.Width - P2.Width) * 1000 AS Width ,
        P1.Unit ,
        P1.date
FROM    @temptbl AS P1
        INNER JOIN @temptbl AS P2 ON P1.ItemId = P2.ItemId
                                     AND P1.ItemNo = P2.ItemNo
                                     AND P1.ItemLocation = P2.ItemLocation
WHERE   P1.ItemProcess = 'P1'
        AND P2.ItemProcess = 'P2'

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EDIT

To make use of indexes, you will need to change your table variable to a temporary table

CREATE TABLE #temptbl
(
    ItemId varchar(50),
    ItemLocation varchar(50),
    ItemNo varchar(50),
    Width real,
    Unit varchar(50),
    date DATETIME,
    ItemProcess INT,
    SubId INT
)

CREATE NONCLUSTERED INDEX Index01 ON #temptbl
(
    ItemProcess ASC,
    ItemId ASC,
    ItemLocation ASC,
    ItemNo ASC
)
INCLUDE ( SubId,Width,Unit,date)
GO

That should speed you up a little.

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John Petrak's answer is the best query for this case. If the speed is still now acceptable, maybe you can store @temptbl at a temporary real table, and create the related index on those four columns.