GitHub user gatorsmile opened a pull request:
https://github.com/apache/spark/pull/15523
[SPARK-17981] [SPARK-17957] [SQL] Incorrectly Set Nullability to False in
FilterExec
### What changes were proposed in this pull request?
When `FilterExec` contains `isNotNull`, which could be inferred and pushed
down or users specified, we convert the nullability of the involved columns if
the top-layer expression is null-intolerant. However, this is not correct, if
the top-layer expression is not a leaf expression, it could still tolerate the
null when it has null-tolerant child expressions.
For example, `cast(coalesce(a#5, a#15) as double)`. Although `cast` is a
null-intolerant expression, but obviously` coalesce` is null-tolerant. Thus, it
could eat null.
When the nullability is wrong, we could generate incorrect results in
different cases. For example,
```Scala
val df1 = Seq((1, 2), (2, 3)).toDF("a", "b")
val df2 = Seq((2, 5), (3, 4)).toDF("a", "c")
val joinedDf = df1.join(df2, Seq("a"), "outer").na.fill(0)
val df3 = Seq((3, 1)).toDF("a", "d")
joinedDf.join(df3, "a").show
```
The optimized plan is like
```
Project [a#29, b#30, c#31, d#42]
+- Join Inner, (a#29 = a#41)
:- Project [cast(coalesce(cast(coalesce(a#5, a#15) as double), 0.0) as
int) AS a#29, cast(coalesce(cast(b#6 as double), 0.0) as int) AS b#30,
cast(coalesce(cast(c#16 as double), 0.0) as int) AS c#31]
: +- Filter isnotnull(cast(coalesce(cast(coalesce(a#5, a#15) as
double), 0.0) as int))
: +- Join FullOuter, (a#5 = a#15)
: :- LocalRelation [a#5, b#6]
: +- LocalRelation [a#15, c#16]
+- LocalRelation [a#41, d#42]
```
Without the fix, it returns an empty result. With the fix, it can return a
correct answer:
```
+---+---+---+---+
| a| b| c| d|
+---+---+---+---+
| 3| 0| 4| 1|
+---+---+---+---+
```
### How was this patch tested?
Added test cases to verify the nullability changes in FilterExec. Also
added a test case for verifying the reported incorrect result.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/gatorsmile/spark nullabilityFilterExec
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15523.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 #15523
----
commit 54c3cc849e91b9bedc6379e04edc9e23245be760
Author: gatorsmile <gatorsm...@gmail.com>
Date: 2016-10-17T23:29:43Z
fix
----
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