GitHub user hvanhovell opened a pull request:
https://github.com/apache/spark/pull/15348
[SPARK-17758][SQL] Last returns wrong result in case of empty partition
## What changes were proposed in this pull request?
The result of the `Last` function can be wrong when the last partition
processed is empty. It can return `null` instead of the expected value. For
example, this can happen when we process partitions in the following order:
```
- Partition 1 [Row1, Row2]
- Partition 2 [Row3]
- Partition 3 []
```
In this case the `Last` function will currently return a null, instead of
the value of `Row3`.
This PR fixes this by adding a `valueSet` flag to the `Last` function.
## How was this patch tested?
We only used end to end tests for `DeclarativeAggregateFunction`s. I have
added an evaluator for these functions so we can tests them in catalyst. I have
added a `LastTestSuite` to test the `Last` aggregate function.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/hvanhovell/spark SPARK-17758
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15348.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 #15348
----
commit 1f0bb1b10558545c29f717162fc3a59855cc96b6
Author: Herman van Hovell <[email protected]>
Date: 2016-10-04T03:02:47Z
Fix Last aggregate function.
commit 893fff5fa9f229643907f23a548f4e32564b2bb0
Author: Herman van Hovell <[email protected]>
Date: 2016-10-04T17:56:06Z
Add tests for Last aggregate function
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