[GitHub] [spark] aokolnychyi commented on a change in pull request #31835: [SPARK-34741][SQL] MergeIntoTable should avoid ambiguous reference in UpdateAction

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aokolnychyi commented on a change in pull request #31835:
URL: https://github.com/apache/spark/pull/31835#discussion_r594757442



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File path: sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/AnalysisSuite.scala
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@@ -671,6 +671,19 @@ class AnalysisSuite extends AnalysisTest with Matchers {
       Project(Seq(UnresolvedAttribute("temp0.a"), UnresolvedAttribute("temp1.a")), join))
   }
 
+  test("SPARK-34741: Avoid ambiguous reference in MergeIntoTable") {
+    val cond = 'a > 1
+    assertAnalysisError(

Review comment:
       I am not sure I got it. Spark resolves keys in UPDATE assignments using only the target table and the values using both the target and the source table. If we encounter `UPDATE SET a = a`, it seems reasonable to get an exception as the value is indeed ambiguous.
   
   But how does the dedup step helps us here? The test below in `ReplaceNullWithFalseInPredicateSuite` covers a case like `UPDATE SET a = source.a` which is not ambiguous. Will that test succeed even without the dedup logic added in this PR?




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