GitHub user cloud-fan opened a pull request:

    https://github.com/apache/spark/pull/16100

    [SPARK-18674][SQL] improve the error message of natural join

    ## What changes were proposed in this pull request?
    
    The current error message of USING join is quite confusing, for example:
    ```
    scala> val df1 = List(1,2,3).toDS.withColumnRenamed("value", "c1")
    df1: org.apache.spark.sql.DataFrame = [c1: int]
    
    scala> val df2 = List(1,2,3).toDS.withColumnRenamed("value", "c2")
    df2: org.apache.spark.sql.DataFrame = [c2: int]
    
    scala> df1.join(df2, usingColumn = "c1")
    org.apache.spark.sql.AnalysisException: using columns ['c1] can not be 
resolved given input columns: [c1, c2] ;;
    'Join UsingJoin(Inner,List('c1))
    :- Project [value#1 AS c1#3]
    :  +- LocalRelation [value#1]
    +- Project [value#7 AS c2#9]
       +- LocalRelation [value#7]
    ```
    
    after this PR, it becomes:
    ```
    scala> val df1 = List(1,2,3).toDS.withColumnRenamed("value", "c1")
    df1: org.apache.spark.sql.DataFrame = [c1: int]
    
    scala> val df2 = List(1,2,3).toDS.withColumnRenamed("value", "c2")
    df2: org.apache.spark.sql.DataFrame = [c2: int]
    
    scala> df1.join(df2, usingColumn = "c1")
    org.apache.spark.sql.AnalysisException: USING column `c1` can not be 
resolved with the right join side, the right output is: [c2];
    ```
    
    ## How was this patch tested?
    
    updated tests

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/cloud-fan/spark natural

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/spark/pull/16100.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 #16100
    
----
commit 94618392045e86498902cb779b07fe88cf10e6de
Author: Wenchen Fan <wenc...@databricks.com>
Date:   2016-12-01T14:21:39Z

    improve the error message of natural join

----


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