refactor

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

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

@@ -850,16 +850,7 @@ private void projectPlusOverriding(
     List<String> originalFieldNames = context.relBuilder.peek().getRowType().getFieldNames();
     List<RexNode> toOverrideList =
         originalFieldNames.stream()
-            .filter(
-                originalName ->
-                    newNames.stream()
-                        .anyMatch(
-                            newName ->
-                                // Match exact field names (e.g., "age" == "age")
-                                // OR nested paths (e.g., "resource.attributes..." starts with
-                                // "resource")
-                                newName.equals(originalName)
-                                    || newName.startsWith(originalName + ".")))
+            .filter(originalName -> shouldOverrideField(originalName, newNames))
             .map(a -> (RexNode) context.relBuilder.field(a))
             .toList();
     // 1. add the new fields, For example "age0, country0"
@@ -879,6 +870,17 @@ private void projectPlusOverriding(
     context.relBuilder.rename(expectedRenameFields);
   }
 
+  private boolean shouldOverrideField(String originalName, List<String> newNames) {
+    return newNames.stream()
+        .anyMatch(
+            newName ->
+                // Match exact field names (e.g., "age" == "age") for flat fields
+                newName.equals(originalName)
+                    // OR match nested paths (e.g., "resource.attributes..." starts with
+                    // "resource.")
+                    || newName.startsWith(originalName + "."));
+  }
+
   private List<List<RexInputRef>> extractInputRefList(List<RelBuilder.AggCall> aggCalls) {
     return aggCalls.stream()
         .map(RelBuilder.AggCall::over)