[
https://issues.apache.org/jira/browse/SPARK-17154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15465226#comment-15465226
]
Wenchen Fan commented on SPARK-17154:
-------------------------------------
can you check if your design satisfies following requirements?
1. self-join issue should be resolved(at least give a better error message)
2. can reference same-name column from different dataframes, e.g.
{code}
val df1 = ...
val df2 = ...
val joined = df1.join(df2, (df1("a") + 1) === df2("a"))
joined.drop(df2("a"))
{code}
3. can reference column from previous dataframe, e.g.
{code}
val df = ...
df.filter(df("a") > 0).filter(df("b") > 0).filter(df("c") === 1)
{code}
> Wrong result can be returned or AnalysisException can be thrown after
> self-join or similar operations
> -----------------------------------------------------------------------------------------------------
>
> Key: SPARK-17154
> URL: https://issues.apache.org/jira/browse/SPARK-17154
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.6.2, 2.0.0
> Reporter: Kousuke Saruta
> Attachments: Solution_Proposal_SPARK-17154.pdf
>
>
> When we join two DataFrames which are originated from a same DataFrame,
> operations to the joined DataFrame can fail.
> One reproducible example is as follows.
> {code}
> val df = Seq(
> (1, "a", "A"),
> (2, "b", "B"),
> (3, "c", "C"),
> (4, "d", "D"),
> (5, "e", "E")).toDF("col1", "col2", "col3")
> val filtered = df.filter("col1 != 3").select("col1", "col2")
> val joined = filtered.join(df, filtered("col1") === df("col1"), "inner")
> val selected1 = joined.select(df("col3"))
> {code}
> In this case, AnalysisException is thrown.
> Another example is as follows.
> {code}
> val df = Seq(
> (1, "a", "A"),
> (2, "b", "B"),
> (3, "c", "C"),
> (4, "d", "D"),
> (5, "e", "E")).toDF("col1", "col2", "col3")
> val filtered = df.filter("col1 != 3").select("col1", "col2")
> val rightOuterJoined = filtered.join(df, filtered("col1") === df("col1"),
> "right")
> val selected2 = rightOuterJoined.select(df("col1"))
> selected2.show
> {code}
> In this case, we will expect to get the answer like as follows.
> {code}
> 1
> 2
> 3
> 4
> 5
> {code}
> But the actual result is as follows.
> {code}
> 1
> 2
> null
> 4
> 5
> {code}
> The cause of the problems in the examples is that the logical plan related to
> the right side DataFrame and the expressions of its output are re-created in
> the analyzer (at ResolveReference rule) when a DataFrame has expressions
> which have a same exprId each other.
> Re-created expressions are equally to the original ones except exprId.
> This will happen when we do self-join or similar pattern operations.
> In the first example, df("col3") returns a Column which includes an
> expression and the expression have an exprId (say id1 here).
> After join, the expresion which the right side DataFrame (df) has is
> re-created and the old and new expressions are equally but exprId is renewed
> (say id2 for the new exprId here).
> Because of the mismatch of those exprIds, AnalysisException is thrown.
> In the second example, df("col1") returns a column and the expression
> contained in the column is assigned an exprId (say id3).
> On the other hand, a column returned by filtered("col1") has an expression
> which has the same exprId (id3).
> After join, the expressions in the right side DataFrame are re-created and
> the expression assigned id3 is no longer present in the right side but
> present in the left side.
> So, referring df("col1") to the joined DataFrame, we get col1 of right side
> which includes null.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
