Bug: Ambiguous Self-Join detected only on right dataframe
Status: Resolved | Priority: Major | Resolution: Fixed
Created: 28/Sep/21 08:20
Affects Version/s: 3.1.2

When joining two dataframes, if they share the same lineage and one dataframe is a transformation of the other, Ambiguous Self Join detection only works when transformed dataframe is the right dataframe. 

For instance {{df1}} and {{df2}} where {{df2}} is a filtered {{df1}}, Ambiguous Self Join detection only works when {{df2}} is the right dataframe:

- {{df1.join(df2, ...)}} correctly fails with Ambiguous Self Join error
- {{df2.join(df1, ...)}} returns a valid dataframe

h1. Minimum Reproducible example
h2. Code
{code:scala}
import sparkSession.implicit._

val df1 = Seq((1, 2, "A1"),(2, 1, "A2")).toDF("key1", "key2", "value")

val df2 = df1.filter($"value" === "A2")

df2.join(df1, df1("key1") === df2("key2")).show()
{code}
h2. Expected Result

Throw the following exception:

{code}
Exception in thread "main" org.apache.spark.sql.AnalysisException: Column key2#11 are ambiguous. It's probably because you joined several Datasets together, and some of these Datasets are the same. This column points to one of the Datasets but Spark is unable to figure out which one. Please alias the Datasets with different names via `Dataset.as` before joining them, and specify the column using qualified name, e.g. `df.as("a").join(df.as("b"), $"a.id" > $"b.id")`. You can also set spark.sql.analyzer.failAmbiguousSelfJoin to false to disable this check.
	at org.apache.spark.sql.execution.analysis.DetectAmbiguousSelfJoin$.apply(DetectAmbiguousSelfJoin.scala:157)
	at org.apache.spark.sql.execution.analysis.DetectAmbiguousSelfJoin$.apply(DetectAmbiguousSelfJoin.scala:43)
	at org.apache.spark.sql.catalyst.rules.RuleExecutor.$anonfun$execute$2(RuleExecutor.scala:216)
	at scala.collection.LinearSeqOptimized.foldLeft(LinearSeqOptimized.scala:126)
	at scala.collection.LinearSeqOptimized.foldLeft$(LinearSeqOptimized.scala:122)
	at scala.collection.immutable.List.foldLeft(List.scala:91)
	at org.apache.spark.sql.catalyst.rules.RuleExecutor.$anonfun$execute$1(RuleExecutor.scala:213)
	at org.apache.spark.sql.catalyst.rules.RuleExecutor.$anonfun$execute$1$adapted(RuleExecutor.scala:205)
	at scala.collection.immutable.List.foreach(List.scala:431)
	at org.apache.spark.sql.catalyst.rules.RuleExecutor.execute(RuleExecutor.scala:205)
	at org.apache.spark.sql.catalyst.analysis.Analyzer.org$apache$spark$sql$catalyst$analysis$Analyzer$$executeSameContext(Analyzer.scala:196)
	at org.apache.spark.sql.catalyst.analysis.Analyzer.execute(Analyzer.scala:190)
	at org.apache.spark.sql.catalyst.analysis.Analyzer.execute(Analyzer.scala:155)
	at org.apache.spark.sql.catalyst.rules.RuleExecutor.$anonfun$executeAndTrack$1(RuleExecutor.scala:183)
	at org.apache.spark.sql.catalyst.QueryPlanningTracker$.withTracker(QueryPlanningTracker.scala:88)
	at org.apache.spark.sql.catalyst.rules.RuleExecutor.executeAndTrack(RuleExecutor.scala:183)
	at org.apache.spark.sql.catalyst.analysis.Analyzer.$anonfun$executeAndCheck$1(Analyzer.scala:174)
	at org.apache.spark.sql.catalyst.plans.logical.AnalysisHelper$.markInAnalyzer(AnalysisHelper.scala:228)
	at org.apache.spark.sql.catalyst.analysis.Analyzer.executeAndCheck(Analyzer.scala:173)
	at org.apache.spark.sql.execution.QueryExecution.$anonfun$analyzed$1(QueryExecution.scala:73)
	at org.apache.spark.sql.catalyst.QueryPlanningTracker.measurePhase(QueryPlanningTracker.scala:111)
	at org.apache.spark.sql.execution.QueryExecution.$anonfun$executePhase$1(QueryExecution.scala:143)
	at org.apache.spark.sql.SparkSession.withActive(SparkSession.scala:775)
	at org.apache.spark.sql.execution.QueryExecution.executePhase(QueryExecution.scala:143)
	at org.apache.spark.sql.execution.QueryExecution.analyzed$lzycompute(QueryExecution.scala:73)
	at org.apache.spark.sql.execution.QueryExecution.analyzed(QueryExecution.scala:71)
	at org.apache.spark.sql.execution.QueryExecution.assertAnalyzed(QueryExecution.scala:63)
	at org.apache.spark.sql.Dataset$.$anonfun$ofRows$1(Dataset.scala:90)
	at org.apache.spark.sql.SparkSession.withActive(SparkSession.scala:775)
	at org.apache.spark.sql.Dataset$.ofRows(Dataset.scala:88)
	at org.apache.spark.sql.Dataset.withPlan(Dataset.scala:3715)
	at org.apache.spark.sql.Dataset.join(Dataset.scala:1079)
	at org.apache.spark.sql.Dataset.join(Dataset.scala:1041)
 ...
{code}
h2. Actual result

Empty dataframe:
{code:java}
+----+----+-----+----+----+-----+
|key1|key2|value|key1|key2|value|
+----+----+-----+----+----+-----+
+----+----+-----+----+----+-----+
{code}