address comments from peng

Signed-off-by: Jialiang Liang <jiallian@amazon.com>

Author: RyanL1997

core/src/main/java/org/opensearch/sql/calcite/CalciteRelNodeVisitor.java

@@ -858,7 +858,6 @@ public RelNode visitPatterns(Patterns node, CalcitePlanContext context) {
   @Override
   public RelNode visitEval(Eval node, CalcitePlanContext context) {
     visitChildren(node, context);
-
     node.getExpressionList()
         .forEach(
             expr -> {
@@ -2246,10 +2245,9 @@ private RelNode mergeTableAndResolveColumnConflict(
   @Override
   public RelNode visitMultisearch(Multisearch node, CalcitePlanContext context) {
     List<RelNode> subsearchNodes = new ArrayList<>();
-
     for (UnresolvedPlan subsearch : node.getSubsearches()) {
       UnresolvedPlan prunedSubSearch = subsearch.accept(new EmptySourcePropagateVisitor(), null);
-      analyze(prunedSubSearch, context);
+      prunedSubSearch.accept(this, context);
       subsearchNodes.add(context.relBuilder.build());
     }
 

core/src/main/java/org/opensearch/sql/executor/QueryService.java

@@ -56,6 +56,9 @@
 @AllArgsConstructor
 @Log4j2
 public class QueryService {
+  private static final HepProgram FILTER_MERGE_PROGRAM =
+      new HepProgramBuilder().addRuleInstance(FilterMergeRule.Config.DEFAULT.toRule()).build();
+
   private final Analyzer analyzer;
   private final ExecutionEngine executionEngine;
   private final Planner planner;
@@ -270,9 +273,7 @@ public RelNode analyze(UnresolvedPlan plan, CalcitePlanContext context) {
    * the rest of optimization.
    */
   private RelNode mergeAdjacentFilters(RelNode relNode) {
-    HepProgram program =
-        new HepProgramBuilder().addRuleInstance(FilterMergeRule.Config.DEFAULT.toRule()).build();
-    HepPlanner planner = new HepPlanner(program);
+    HepPlanner planner = new HepPlanner(FILTER_MERGE_PROGRAM);
     planner.setRoot(relNode);
     return planner.findBestExp();
   }