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Posted to github@arrow.apache.org by "viirya (via GitHub)" <gi...@apache.org> on 2023/03/21 21:01:07 UTC
[GitHub] [arrow-datafusion] viirya opened a new issue, #5674: Decimal multiply kernel may cause precision loss
viirya opened a new issue, #5674:
URL: https://github.com/apache/arrow-datafusion/issues/5674
**Describe the bug**
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Currently decimal multiply kernel (`multiply_dyn_decimal`) sets original scale by a divide operation. It tries to restore the scale assuming lhs and rhs have the same scale. For example, multiply two decimals (-491, -591) with precision/scale (5, 2), it will divide 290181 by 2 to get the result 29.01 with same precision/scale (5, 2). But by doing this, it loses decimal precision. For example, in Spark, the answer is 29.0181 with precision/scale (11, 4).
**To Reproduce**
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**Expected behavior**
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I'd expect that it behaves like Spark as mentioned above.
**Additional context**
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[GitHub] [arrow-datafusion] mustafasrepo commented on issue #5674: Decimal multiply kernel may cause precision loss
Posted by "mustafasrepo (via GitHub)" <gi...@apache.org>.
mustafasrepo commented on issue #5674:
URL: https://github.com/apache/arrow-datafusion/issues/5674#issuecomment-1480670412
>
I guess you meant -4.91 and -5.91 instead of (-491 and -591).
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[GitHub] [arrow-datafusion] Dandandan commented on issue #5674: Decimal multiply kernel may cause precision loss
Posted by "Dandandan (via GitHub)" <gi...@apache.org>.
Dandandan commented on issue #5674:
URL: https://github.com/apache/arrow-datafusion/issues/5674#issuecomment-1481503030
Also see
https://github.com/apache/arrow-datafusion/issues/5143
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[GitHub] [arrow-datafusion] Dandandan closed issue #5674: Decimal multiply kernel may cause precision loss
Posted by "Dandandan (via GitHub)" <gi...@apache.org>.
Dandandan closed issue #5674: Decimal multiply kernel may cause precision loss
URL: https://github.com/apache/arrow-datafusion/issues/5674
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[GitHub] [arrow-datafusion] viirya commented on issue #5674: Decimal multiply kernel may cause precision loss
Posted by "viirya (via GitHub)" <gi...@apache.org>.
viirya commented on issue #5674:
URL: https://github.com/apache/arrow-datafusion/issues/5674#issuecomment-1481474306
Yes, -491 and -591 are their i128 representation in the array with precision/scale (5, 2).
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