Question

A wrong percentage has been applied to a field (TotalPercentageAmount) and I need to correct it.
Given 2 fields Amount and TotalPercentageAmount how can I calculate what percentage was applied?
I need to work out percentage applied to TotalPercentageAmount and UPDATE the column with correct percentage.

Little script I have created to mimin my scenario . Table created contains wrong TotalPercentageAmount!!!

        CREATE TABLE [dbo].[SalesReportTest](
            [Id] [int] NOT NULL,
            [Amount] [decimal](18, 4) NOT NULL,
            [TotalPercentageAmount] [decimal](18, 4) NOT NULL,
         CONSTRAINT [PK_SalesReportTest] PRIMARY KEY CLUSTERED 
        (
            [Id] ASC
        )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
        ) ON [PRIMARY]


        GO
        SET NOCOUNT ON;
        SET XACT_ABORT ON;
        GO

        BEGIN TRANSACTION;
        INSERT INTO [dbo].[SalesReportTest]([Id], [Amount], [TotalPercentageAmount])
        SELECT 1, 55.0000, 52.0300 UNION ALL
        SELECT 2, 440.0000, 416.2200 UNION ALL
        SELECT 3, 300.0000, 283.8000 UNION ALL
        SELECT 4, -55.0000, -52.0300 UNION ALL
        SELECT 5, 98.0000, 92.7000 UNION ALL
        SELECT 6, -10.0000, -9.4600
        COMMIT;
        RAISERROR (N'[dbo].[SalesReportTest]: Insert Batch: 1.....Done!', 10, 1) WITH NOWAIT;
        GO

Answer 1

You can try the following to determine the percentage used. However, it appears that there is some precision loss because the Amount column appears to be truncated. I also include a column that demonstrates the 5.72% calc in your sample data.

SELECT *, 
    CAST ((Amount / TotalPercentageAmount - 1) * 100 AS DECIMAL (5, 2)) as Pct,
    CAST (TotalPercentageAmount * 1.0572 AS INT) Amt_Calc
FROM [SalesReportTest]