Alter Top 10 to equal 100 when rounded to 1 decimal place

Question

I'm building a Top 10 for a report for some management information which ends with the following script:

IF @ReportType = 'SectorEQ'

BEGIN
/* Final Select with roll up for total per portfolio */
    SELECT 
            CONVERT(VARCHAR, ReportingDate, 103)    AS ReportingDate
        ,   PortfolioID                             AS FundCode
        ,   PortfolioNme                            AS FundName

        ,   CASE 
                WHEN GROUPING_ID(ReportingDate, PortfolioID, PortfolioNme, Sector, [Rank], [Weight]) = 7 THEN 'Total'
                ELSE Sector
                END                                 AS Sector

        ,   CASE 
                WHEN GROUPING_ID(ReportingDate, PortfolioID, PortfolioNme, Sector, [Rank], [Weight]) = 7 THEN 102
                ELSE [Rank]
            END                                     AS [Rank]

        ,   CAST(SUM([Weight]) AS DECIMAL(22,1))    AS Percentage

    FROM @FinalOutputEQ_CS

    GROUP BY    ReportingDate
            ,   PortfolioID
            ,   PortfolioNme
            ,   Sector
            ,   [Rank]
            ,   [Weight] WITH ROLLUP

    HAVING GROUPING_ID(ReportingDate, PortfolioID, PortfolioNme, Sector, [Rank], [Weight]) IN (1,7)

    ORDER BY    ReportingDate
            ,   PortfolioID
            ,   [Rank]

As you will see, the percentage is rounded to 1 decimal place which can potentially cause rounding issues because the sum of the percentage to 1 decimal place could be less than or greater than 100, ie 100.1 or 99.9. What i need to do is to ensure that the rounded to 1 decimal place percentages all equal to 100.0.

What i would like to do is have a check to see that the sum of the rounded percentages is equal to 100.0, if it isn't then to take the Top 1 and minus the difference from its percentage.

I've had a few ideas as to how to do this, but i'm wondering what would be the best method to ensure this run quickly and efficiently without slowing the proc down?

EDIT: Example Table

ReportingDate   FundCode    FundName    Sector                   Rank   Percentage
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Consumer Discretionary      1   16.1
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Health Care                 2   13.8
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Information Technology      3   11.8
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Telecommunication Services  4   10.3
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Consumer Staples            5   10.1
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Industrials                 6   8.7
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Financials                  7   6.8
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Materials                   8   6.5
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Energy                      9   5.2
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Utilities                   10  0.7
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Cash and Bonds              101 10.1
28/02/2013  XXXXXXXX    XXXXXXXXXXXXXXX Total                       102 100.1

Answer 1

The only solution i could work out for this is to create the script below which basically summed up the detail to give a total. Then after my CTE i subtracted this from the top 1 and the total:

IF @ReportType = 'SectorEQ'

BEGIN
    INSERT INTO @RoundingDifference
        SELECT
                PortfolioID
            ,   CAST(SUM([Weight])-100 AS DECIMAL(22,1)) AS [Weight]

        FROM @FinalOutputEQ_CS

        WHERE Sector <> 'Total'

        GROUP BY        
                ReportingDate
            ,   PortfolioID
            ,   PortfolioNme

END

IF @ReportType = 'SectorEQ'

BEGIN
;;WITH CTE AS
    (
/* Final Select with roll up for total per portfolio */
    SELECT 
            CONVERT(VARCHAR, ReportingDate, 103)    AS ReportingDate
        ,   PortfolioID                             AS FundCode
        ,   PortfolioNme                            AS FundName

        ,   CASE 
                WHEN GROUPING_ID(ReportingDate, PortfolioID, PortfolioNme, Sector, [Rank], [Weight]) = 7 THEN 'Total'
                ELSE Sector
                END                                 AS Sector

        ,   CASE 
                WHEN GROUPING_ID(ReportingDate, PortfolioID, PortfolioNme, Sector, [Rank], [Weight]) = 7 THEN 102
                ELSE [Rank]
            END                                     AS [Rank]

        ,   CAST(SUM([Weight]) AS DECIMAL(22,1))    AS Percentage

    FROM @FinalOutputEQ_CS

    GROUP BY    ReportingDate
            ,   PortfolioID
            ,   PortfolioNme
            ,   Sector
            ,   [Rank]
            ,   [Weight] WITH ROLLUP

    HAVING GROUPING_ID(ReportingDate, PortfolioID, PortfolioNme, Sector, [Rank], [Weight]) IN (1,7)
    )
    SELECT 
        ReportingDate
    ,   FundCode
    ,   FundName
    ,   Sector
    ,   [Rank]

    ,   CASE 
            WHEN [Rank]IN (1,102) THEN Percentage - RD.[Weight]
            ELSE Percentage
        END     AS Percentage

    FROM CTE AS CTE

        INNER JOIN @RoundingDifference AS RD
        ON RD.PortfolioID = CTE.FundCode

    ORDER BY    ReportingDate
            ,   FundCode
            ,   [Rank]

END

Answer 2

Could just just not have a decimal type go to a tenth place?

EG:

declare @decimal decimal (16,4) = 123456.7890;    ;

select cast(@decimal as decimal(16,0))

INSTEAD OF

select cast(@decimal as decimal(16,1))

Also why are you having the values go out 22 values? (first position in decimal type) That is lot of data to store if you are worrying about the proc being efficient. I usually am stingy with the first number and rarely exceed 16 except with very large data returns.

EDIT for rounding the tenth place:

declare @decimal decimal (16,1) = 123456.5;   -- you can change this as needed to see how it will change

-- if you want to do rounding then you need to determine if the tenth position is above or greater than five
-- you could do this in a function if you want.  You need to determine a return of 1 or 0 based on rounding
declare @logic int = case when right(@decimal,1) >= 5 then 1 else 0 end

-- find the integer value WITHOUT the decimal places and then add the logic variable
select left(@decimal, len(@decimal) - 2) + @logic as Rounded