[GitHub] [spark] wangyum commented on a change in pull request #31857: [SPARK-28220][SQL] Push down the foldable predicate to both sides of Join

[GitBox <gi...@apache.org>]

wangyum commented on a change in pull request #31857:
URL: https://github.com/apache/spark/pull/31857#discussion_r595688798



##########
File path: sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/FilterPushdownSuite.scala
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@@ -1384,4 +1384,14 @@ class FilterPushdownSuite extends PlanTest {
       condition = Some("x.a".attr === "z.a".attr)).analyze
     comparePlans(optimized, correctAnswer)
   }
+
+  test("SPARK-28220: Push down the foldable predicate to both sides of Join") {
+    val x = testRelation.subquery('x)
+    val y = testRelation.subquery('y)
+    val originalQuery = x.join(y, condition = Some(false))
+
+    val optimized = Optimize.execute(originalQuery.analyze)
+    val correctAnswer = x.where(false).join(y.where(false), condition = None).analyze
+    comparePlans(optimized, correctAnswer.analyze)

Review comment:
       We use `Inner` join to do test because it need `PruneFilters` if use `LeftOuter` join:
   ```scala
   val x = testRelation.subquery('x)
   val y = testRelation.subquery('y)
   val originalQuery = x.join(y, LeftOuter, condition = Some(false))
   
   val optimized = Optimize.execute(originalQuery.analyze)
   val correctAnswer = x.join(y.where(false), LeftOuter, condition = None).analyze
   comparePlans(optimized, correctAnswer.analyze)
   ```
   Error:
   ```
   == FAIL: Plans do not match ===
   !'Join LeftOuter, false                            'Join LeftOuter
    :- LocalRelation <empty>, [a#0, b#0, c#0]         :- LocalRelation <empty>, [a#0, b#0, c#0]
    +- Filter false                                   +- Filter false
   !   +- Filter false                                   +- LocalRelation <empty>, [a#0, b#0, c#0]
   !      +- LocalRelation <empty>, [a#0, b#0, c#0]   
   ```




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