Github user davies commented on the pull request:
https://github.com/apache/spark/pull/8409#issuecomment-134488372
@yhuai For Add/Sub/Multiply, we should not lose precision (we can't reduce
the scale of result, prefer overflow), but for division, we can't keep all the
precision under zero anyway, then we could have a maximum scale, or preserve
the range first.
From MS SQL Serverï¼ https://msdn.microsoft.com/en-us/library/ms190476.aspx
```* The result precision and scale have an absolute maximum of 38. When a
result precision is greater than 38, the corresponding scale is reduced to
prevent the integral part of a result from being truncated.
```
To be safe, I think we should only do this for division, or we will lose
precision silently for add/sub/multiply (it does overflow in Hive).
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