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https://issues.apache.org/jira/browse/SPARK-13801?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15219137#comment-15219137
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Denton Cockburn commented on SPARK-13801:
-----------------------------------------
I'm unsure if this is the same issue, but I hit upon this problem.
{code}
import sqlContext.implicits._
import org.apache.spark.sql.functions._
val df = Seq((1, 1,1,1), (2,2,2,2)).toDF("a", "b", "c", "d")
val f = df.where($"a" === 1).alias("a")
val s = df.where($"a" === 2).alias("b")
f.join(s, f("b") === s("b") and f("c") === s("c"),
"outer").select(coalesce(f("b"), s("b")), coalesce(f("c"), s("c")),
coalesce(f("d"), s("d"))).show
{code}
The output is:
{code}
|coalesce(b,b)|coalesce(c,c)|coalesce(d,d)|
+-------------+-------------+-------------+
| 1| 1| 1|
| null| null| null|
+-------------+-------------+-------------+
{code}
Instead of:
{code}
|coalesce(b,b)|coalesce(c,c)|coalesce(d,d)|
+-------------+-------------+-------------+
| 1| 1| 1|
| 2| 2| 2|
+-------------+-------------+-------------+
{code}
> DataFrame.col should return unresolved attribute
> ------------------------------------------------
>
> Key: SPARK-13801
> URL: https://issues.apache.org/jira/browse/SPARK-13801
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Reporter: Wenchen Fan
>
> Recently I saw some JIRAs complain about wrong result when using DataFrame
> API. After checking their queries, I found it was caused by un-direct
> self-join and they build wrong join conditions. For example:
> {code}
> val df = ...
> val df2 = df.filter(...)
> df.join(df2, (df("key") + 1) === df2("key"))
> {code}
> In this case, the confusing part is: df("key") and df2("key2") reference to
> the same column, while df and df2 are different DataFrames.
> I think the biggest problem is, we give users the resolved attribute.
> However, resolved attribute is not real column, as logical plan's output may
> change. For example, we will generate new output for the right child in
> self-join.
> My proposal is: `DataFrame.col` should always return unresolved attribute. We
> can still do the resolution to make sure the given column name is resolvable,
> but don't return the resolved one, just get the name out and wrap it with
> UnresolvedAttribute.
> Now if users run the example query I gave at the beginning, they will get
> analysis exception, and they will understand they need to alias df and df2
> before join.
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