SQL Wrong Result Values On Money Sum

Question

Using Delphi X10 & Absolute Database SQL92 Compatible. I am using this SQL script :

  SELECT SUM (CREDIT) AS "SUM_CREDIT",
         SUM (DEBIT) AS "SUM_DEBIT",
         SUM (CREDIT) - SUM (DEBIT) AS Balance,
         YearPay,
         IDCustomer,
         DescCredit
    FROM CostumersPayments
GROUP BY YearPay, IDCustomer, DescCredit
  HAVING (SUM (CREDIT) - SUM (DEBIT)) > 0
ORDER BY YearPay;

My table has about 3000 records; the returned result is about 300 records.

The problem is that I get for equal debit with equal credit, balance as 0

Result:

Credit | Debit  | Balance
$ 4,56 | $ 4,56 |    0
$12,12 | $12,12 |    0
$21,6  | $21,6  |    0
.....

This happens for about 30 result records, the others result records are ok.

This is a strange behavior because I want HAVING (SUM (CREDIT) - SUM (DEBIT)) > 0 . So after searching a little I have found that when AS FLOAT converting:

         CAST(SUM (CREDIT) AS FLOAT) AS "SUM_CREDIT",
         CAST(SUM (DEBIT) AS FLOAT) AS "SUM_DEBIT",
         CAST(SUM (CREDIT) - SUM (DEBIT) AS FLOAT) AS "SUM_BALANCE"

The returned results for the 30 same records after the conversion are:

Credit | Debit  | Balance
$ 4,56 | $ 4,56 | 8,88178419700125E-16
$12,12 | $12,12 | 1,77635683940025E-15
$21,6  | $21,60 | 3,5527136788005E-15

In most Balance result the values are 3,5527136788005E-15 and 7,105427357601E-15. The resulting 0's have values 0,000something. I have found the records and retype the debit & credit values. Same result.

The field types are Currency on the Table.

Where is the problem?

Answer 1

I don't know why it returns those values, but a quick fix around would be to discard all those garbage decimals when checking if CREDIT - DEBIT = 0.

 SELECT SUM (CREDIT) AS "SUM_CREDIT",
         SUM (DEBIT) AS "SUM_DEBIT",
         SUM (CREDIT) - SUM (DEBIT) AS Balance,
         YearPay,
         IDCustomer,
         DescCredit
    FROM CostumersPayments
GROUP BY YearPay, IDCustomer, DescCredit
  HAVING cast(SUM (CREDIT) - SUM (DEBIT) as numeric(18, 4)) > 0
ORDER BY YearPay;