[VL] Fix native Union result name (#11832)

Fix native union result use column type name as column name, which lead to same data type column has same data, but is not right result. eg all string columns has same data value as the first string column

const auto name = outRowType->childAt(colIdx)->name();
result name is column type name => Wrong
const auto name = outRowType->nameOf(colIdx);
result name is column name => Correct



Co-authored-by: lifulong <lifulong@zhihu.com>

Author: lifulong

backends-velox/src/test/scala/org/apache/gluten/execution/MiscOperatorSuite.scala

@@ -582,6 +582,55 @@ class MiscOperatorSuite extends VeloxWholeStageTransformerSuite with AdaptiveSpa
     }
   }
 
+  test("native union_all with two level union keeps distinct output columns") {
+    withTempView("union_src_a", "union_src_b", "union_src_c") {
+      Seq(
+        ("valueA", "value1", "value11", "value111"),
+        ("valueA", "value2", "value22", "value222")
+      ).toDF("col1", "col2", "col3", "col4")
+        .createOrReplaceTempView("union_src_a")
+      Seq(
+        ("valueB", "value3", "value33", "value333"),
+        ("valueB", "value4", "value44", "value444")
+      ).toDF("col1", "col2", "col3", "col4")
+        .createOrReplaceTempView("union_src_b")
+
+      withSQLConf(GlutenConfig.NATIVE_UNION_ENABLED.key -> "true") {
+        compareDfResultsAgainstVanillaSpark(
+          () =>
+            spark.sql("""
+                        |with deduplicated_data as (
+                        |  select col1, col2, col3, col4
+                        |  from (
+                        |    select
+                        |      u.col1,
+                        |      u.col2,
+                        |      u.col3,
+                        |      u.col4,
+                        |      row_number() over (partition by u.col2 order by u.col5 desc) as rn
+                        |    from (
+                        |      select col1, col2, col3, col4, 98 as col5 from union_src_a
+                        |      union all
+                        |      select col1, col2, col3, col4, 100 as col5 from union_src_b
+                        |    ) u
+                        |  ) t
+                        |  where t.rn = 1
+                        |)
+                        |select col1, col2, col3, col4
+                        |from deduplicated_data
+                        |where col1 != 'valueC'
+                        |union all
+                        |select col1, col2, col3, col4
+                        |from deduplicated_data
+                        |where col1 = 'valueC'
+                        |""".stripMargin),
+          compareResult = true,
+          checkGlutenPlan[UnionExecTransformer]
+        )
+      }
+    }
+  }
+
   test("union two tables") {
     runQueryAndCompare("""
                          |select count(orderkey) from (

cpp/velox/substrait/SubstraitToVeloxPlan.cc

@@ -1244,7 +1244,8 @@ core::PlanNodePtr SubstraitToVeloxPlanConverter::toVeloxPlan(const ::substrait::
       const RowTypePtr outRowType = asRowType(children[0]->outputType());
       std::vector<std::string> outNames;
       for (int32_t colIdx = 0; colIdx < outRowType->size(); ++colIdx) {
-        const auto name = outRowType->childAt(colIdx)->name();
+        // Using field names from the unified output row type instead child type names
+        const auto name = outRowType->nameOf(colIdx);
         outNames.push_back(name);
       }