GitHub user dongjoon-hyun opened a pull request:
https://github.com/apache/spark/pull/14307
[SPARK-16672][SQL] SQLBuilder should not raise exceptions on EXISTS queries
## What changes were proposed in this pull request?
Currently, `SQLBuilder` raises `empty.reduceLeft` exceptions on
*unoptimized* `EXISTS` queries. We had better prevent this.
```scala
scala> sql("CREATE TABLE t1(a int)")
scala> val df = sql("select * from t1 b where exists (select * from t1 a)")
scala> new org.apache.spark.sql.catalyst.SQLBuilder(df).toSQL
java.lang.UnsupportedOperationException: empty.reduceLeft
```
## How was this patch tested?
Pass the Jenkins tests with a new test suite.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/dongjoon-hyun/spark SPARK-16672
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/14307.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 #14307
----
commit 7baab5ef66f2091ba9f33a32b8005c3f85354e6b
Author: Dongjoon Hyun <[email protected]>
Date: 2016-07-21T20:12:58Z
[SPARK-16672][SQL] SQLBuilder should not raise exceptions on EXISTS queries
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