[SPARK-25278][SQL] Avoid duplicated Exec nodes when the same logical plan appears in the query

Author: mgaido91

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/QueryPlanner.scala

@@ -81,7 +81,7 @@ abstract class QueryPlanner[PhysicalPlan <: TreeNode[PhysicalPlan]] {
               childPlans.map { childPlan =>
                 // Replace the placeholder by the child plan
                 candidateWithPlaceholders.transformUp {
-                  case p if p == placeholder => childPlan
+                  case p if p.eq(placeholder) => childPlan
                 }
               }
             }

sql/core/src/test/scala/org/apache/spark/sql/execution/metric/SQLMetricsSuite.scala

@@ -497,6 +497,17 @@ class SQLMetricsSuite extends SparkFunSuite with SQLMetricsTestUtils with Shared
     }
   }
 
+  test("SPARK-25278: output metrics are wrong for plans repeated in the query") {
+    val name = "demo_view"
+    sql(s"CREATE OR REPLACE VIEW $name AS VALUES 1,2")
+    val view = spark.table(name)
+    val union = view.union(view)
+    testSparkPlanMetrics(union, 1, Map(
+      0L -> ("Union" -> Map()),
+      1L -> ("LocalTableScan" -> Map("number of output rows" -> 2L)),
+      2L -> ("LocalTableScan" -> Map("number of output rows" -> 2L))))
+  }
+
   test("writing data out metrics: parquet") {
     testMetricsNonDynamicPartition("parquet", "t1")
   }