MS Access 2003 - sum is producing too many decimal places

Posted on 2011-03-14
Last Modified: 2012-05-11
SELECT tblDrafts.D_CaseNumber, Sum(tblDrafts.D_Amount) AS SumOfD_Amount
FROM tblDrafts
GROUP BY tblDrafts.D_CaseNumber;

produces sum with many decimal digits instead of two digits as defined in the table. By using Round function, it is not giving correct sum in decimal values. Example, the value in table is say 169531.10 and it is showing 169531.09 because it is rounding 169531.09354...
Question by:gpdixit
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LVL 120

Expert Comment

by:Rey Obrero (Capricorn1)
ID: 35128633
try this

SELECT tblDrafts.D_CaseNumber, formatnumber(Sum(tblDrafts.D_Amount),2) AS SumOfD_Amount
FROM tblDrafts
GROUP BY tblDrafts.D_CaseNumber;
LVL 92

Accepted Solution

Patrick Matthews earned 500 total points
ID: 35128832

Unless you are using the Decimal data type for that column with a Scale parameter of two, then you are NOT actually storing your values as numbers with two decimal places--rather, they are merely formatted that way for display.  As such, cap1's suggestion will not necessarily return the correct answer.

Instead, you would have to round each value BEFORE it goes into the sum:

SELECT D_CaseNumber, Sum(Round([D_Amount], 2)) AS SumOfD_Amount
FROM tblDrafts
GROUP BY D_CaseNumber;

Open in new window

That, of course, uses "banker's rounding".  To round Excel-style:

SELECT D_CaseNumber, Sum(Val(Format([D_Amount], "0.00"))) AS SumOfD_Amount
FROM tblDrafts
GROUP BY D_CaseNumber;

Open in new window

Be warned, though, that taking the sum of rounded items is a mathematically dubious idea :)

LVL 50

Expert Comment

by:Gustav Brock
ID: 35129558
Always - always - use data type Currency for currency, amounts, etc.

If you can 't change the fields of the table, convert to Currency at the earliest stage:
  Sum(CCur(tblDrafts.D_Amount)) AS SumOfD_Amount

Open in new window

The reason for your rounding errors is caused by adding positive and negative amounts when these are Single or Double.

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LVL 92

Expert Comment

by:Patrick Matthews
ID: 35129815
I was wondering when your "Spidey sense" would start tingling, gustav :)
LVL 50

Expert Comment

by:Gustav Brock
ID: 35129915
Believe me, it's operating at random!


Author Closing Comment

ID: 35153893
Expert gave two solutions, out of which second solution was acceptable. I tried and and it is successful. Solution was provided in a very short time. Lot of thanks.

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