GitHub user hvanhovell opened a pull request:
https://github.com/apache/spark/pull/17278
[SPARK-19933][SQL] Do not change output of a subquery
## What changes were proposed in this pull request?
The `RemoveRedundantAlias` rule can change the output attributes (the
expression id's to be precise) of a query by eliminating the redundant alias
producing them. This is no problem for a regular query, but can cause problems
for correlated subqueries: The attributes produced by the subquery are used in
the parent plan; changing them will break the parent plan.
This PR fixes this by wrapping a subquery in a `ReturnAnswer` top level
node when it gets optimized. The `RemoveRedundantAlias` rule now recognizes
`ReturnAnswer` and makes aure that the output attributes of the `ReturnAnswer`
node are retained.
## How was this patch tested?
Added a test case to `RemoveRedundantAliasAndProjectSuite` and added a
regression test to `SubquerySuite`.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/hvanhovell/spark SPARK-19933
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/17278.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 #17278
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commit 54cbad15ed17bf9c16b372fb3e5fdf6a8fee69ae
Author: Herman van Hovell <hvanhov...@databricks.com>
Date: 2017-03-13T16:14:47Z
Do not change output of a subquery
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