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Query returns -4.61852778244065E-14 for a number field calculation

Posted on 2014-01-29
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Last Modified: 2014-02-04
I have an invoice table containing a number invoice lines, each with with 3 fields, Debit, Credit, and Amount.  All doubles to 2 dec places.  

Amount is positive for Debits and negative for Credits.  The Invoice looks perfectly normal in the Invoice table.  All values to 2 decimal places.

I have query which groups the transactions by invoice and sums the Amount which should be zero.

However, the query sometimes returns a Sum of Amount such as -4.61852778244065E-14, which makes the invoice out of balance.

Can anyone tell me how to fix this?

Thanks in advance.
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Question by:CRB1609
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5 Comments
 
LVL 61

Expert Comment

by:mbizup
ID: 39819657
Floating point calculations are imprecise (period).

When you are comparing two floating point numbers you should avoid exact comparisons like checking if Field1 = Field2.

Instead, compare for numbers within acceptable 'tolerances'.

For example instead of Field1 = Field2, check for a tolerance such as:

Abs(Field1 - Field2) <  .0001
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LVL 61

Assisted Solution

by:mbizup
mbizup earned 400 total points
ID: 39819664
Regarding your 'Out of balance' issue... you can define a tolerance for your balance as well.

For example, define "Balanced" as somewhere between  -.00001 and + .00001, instead of strictly defining it as 0.
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Expert Comment

by:marlind605
ID: 39819700
Have you tried the rounding when you calculate your number? This is From Microsoft How to Round a Number Up or Down
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LVL 48

Accepted Solution

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Dale Fye earned 1600 total points
ID: 39819845
Change the datatype to Currency instead of double.

or use the ccur( ) conversion function to make the conversion in the query.
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LVL 51

Expert Comment

by:Gustav Brock
ID: 39820097
Yes. Cure your issue at the root. Listen to Dale and act. (No points please).

/gustav
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