GitHub user clockfly opened a pull request:
https://github.com/apache/spark/pull/15171
[SPARK-17617][SQL] Remainder(%) expression.eval returns incorrect result on
double value
## What changes were proposed in this pull request?
Remainder(%) expression's `eval()` returns incorrect result when the
dividend is a big double. The reason is that Remainder converts the double
dividend to decimal to do "%", and that lose precision.
This bug only affects the `eval()` that is used by constant folding, the
codegen path is not impacted.
### Before change
```
scala> spark.sql("select -5083676433652386516D % 10 as a").show
+---+
| a|
+---+
|0.0|
+---+
```
### After change
```
scala> spark.sql("select -5083676433652386516D % 10 as a").show
+----+
| a|
+----+
|-6.0|
+----+
```
## How was this patch tested?
Unit test.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/clockfly/spark SPARK-17617
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15171.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #15171
----
commit 955f49a5bf8e99612ddce95c3a1c10ba2c1400f0
Author: Sean Zhong <seanzh...@databricks.com>
Date: 2016-09-21T00:19:46Z
Fix a % b if a is a double
----
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