update according to review comments

Author: fang-xing-esql

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/analysis/Analyzer.java

@@ -2277,9 +2277,9 @@ private static AggregateMetricDoubleBlockBuilder.Metric getMetric(AggregateFunct
 
     /**
      * Handle union types in UnionAll:
-     * 1. Push down explicit conversion functions into the UnionAll legs
+     * 1. Push down explicit conversion functions into the UnionAll branches
      * 2. Replace the explicit conversion functions with the corresponding attributes in the UnionAll output
-     * 3. Implicitly cast the outputs of the UnionAll legs to the common type if necessary
+     * 3. Implicitly cast the outputs of the UnionAll branches to the common type if necessary
      * 4. Update the attributes referencing the updated UnionAll output
      */
     private static class ResolveUnionTypesInUnionAll extends Rule<LogicalPlan, LogicalPlan> {
@@ -2293,7 +2293,7 @@ private static class ResolveUnionTypesInUnionAll extends Rule<LogicalPlan, Logic
         public LogicalPlan apply(LogicalPlan plan) {
             convertFunctionsToAttributes = new HashMap<>();
             updatedUnionAllOutput = new ArrayList<>();
-            // First push down the conversion functions into the UnionAll legs
+            // First push down the conversion functions into the UnionAll branches
             LogicalPlan planWithConvertFunctionsPushedDown = plan.transformUp(
                 UnionAll.class,
                 unionAll -> maybePushDownConvertFunctions(unionAll, plan)
@@ -2302,7 +2302,7 @@ public LogicalPlan apply(LogicalPlan plan) {
             // Then replace the conversion functions with the corresponding attributes in the UnionAll output
             LogicalPlan planWithConvertFunctionsReplaced = replaceConvertFunctions(planWithConvertFunctionsPushedDown);
 
-            // Next implicitly cast the outputs of the UnionAll legs to the common type if necessary
+            // Next implicitly cast the outputs of the UnionAll branches to the common type if necessary
             LogicalPlan planWithImplicitCasting = planWithConvertFunctionsReplaced.transformUp(
                 UnionAll.class,
                 unionAll -> unionAll.resolved() ? implicitCastingUnionAllOutput(unionAll, plan) : unionAll
@@ -2322,7 +2322,7 @@ private LogicalPlan maybePushDownConvertFunctions(UnionAll unionAll, LogicalPlan
                 return unionAll;
             }
 
-            // push down the conversion functions into the unionAll legs
+            // push down the conversion functions into the unionAll branches
             List<LogicalPlan> newChildren = new ArrayList<>(unionAll.children().size());
             boolean outputChanged = false;
             for (LogicalPlan child : unionAll.children()) {
@@ -2420,7 +2420,7 @@ private LogicalPlan implicitCastingUnionAllOutput(UnionAll unionAll, LogicalPlan
 
             Map<Integer, DataType> indexToCommonType = new HashMap<>();
 
-            // Cast each leg's output to the common type
+            // Cast each branch's output to the common type
             List<LogicalPlan> newChildren = new ArrayList<>(unionAll.children().size());
             boolean outputChanged = false;
             for (LogicalPlan child : unionAll.children()) {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/PushDownFilterAndLimitIntoUnionAll.java

@@ -54,7 +54,7 @@ public LogicalPlan apply(LogicalPlan logicalPlan) {
         );
     }
 
-    /* Push down filters that can be evaluated by the UnionAll child/leg to each child/leg,
+    /* Push down filters that can be evaluated by the UnionAll branch to each branch,
      * so that the filters can be pushed down further to the data source when possible.
      * Filters that cannot be pushed down remain above the UnionAll.
      *

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plan/logical/UnionAll.java

@@ -22,26 +22,23 @@
 
 public class UnionAll extends Fork implements PostOptimizationPlanVerificationAware {
 
-    private final List<Attribute> output;
-
     public UnionAll(Source source, List<LogicalPlan> children, List<Attribute> output) {
         super(source, children, output);
-        this.output = output;
     }
 
     @Override
     public LogicalPlan replaceChildren(List<LogicalPlan> newChildren) {
-        return new UnionAll(source(), newChildren, output);
+        return new UnionAll(source(), newChildren, output());
     }
 
     @Override
     protected NodeInfo<? extends LogicalPlan> info() {
-        return NodeInfo.create(this, UnionAll::new, children(), output);
+        return NodeInfo.create(this, UnionAll::new, children(), output());
     }
 
     @Override
     public UnionAll replaceSubPlans(List<LogicalPlan> subPlans) {
-        return new UnionAll(source(), subPlans, output);
+        return new UnionAll(source(), subPlans, output());
     }
 
     @Override