GitHub user hvanhovell opened a pull request:
https://github.com/apache/spark/pull/14867
[SPARK-17296][SQL] Simplify join parser join processing.
## What changes were proposed in this pull request?
Join processing in the parser relies on the fact that the grammar produces
a right nested trees, for instance the parse tree for `select * from a join b
join c` is expected to produce a tree similar to `JOIN(a, JOIN(b, c))`. However
there are cases in which this (invariant) is violated, like:
```sql
SELECT COUNT(1)
FROM test T1
CROSS JOIN test T2
JOIN test T3
ON T3.col = T1.col
JOIN test T4
ON T4.col = T1.col
```
In this case the parser returns a tree in which Joins are located on both
the left and the right sides of the parent join node.
This PR introduces a different grammar rule which does not make this
assumption. The new rule takes a relation and searches for zero or more joined
relations. As a bonus processing is much easier.
## How was this patch tested?
Existing tests and I have added a regression test to the plan parser suite.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/hvanhovell/spark SPARK-17296
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/14867.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 #14867
----
commit b25e2db00f327ff81f8d243948ef4df77e31af15
Author: Herman van Hovell <[email protected]>
Date: 2016-08-29T20:12:59Z
Simplify join processing.
commit f9cb0d267bf1d4c5f0e16d832e90684236fe74ce
Author: Herman van Hovell <[email protected]>
Date: 2016-08-29T20:21:58Z
Merge remote-tracking branch 'apache-github/master' into SPARK-17296
# Conflicts:
#
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala
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