[GitHub] [doris] jackwener commented on a diff in pull request #18687: [enhance](Nereids): memo get needReplaceChild by getParentGroupExpressions().

["jackwener (via GitHub)" <gi...@apache.org>]

jackwener commented on code in PR #18687:
URL: https://github.com/apache/doris/pull/18687#discussion_r1171265536


##########
fe/fe-core/src/main/java/org/apache/doris/nereids/memo/Memo.java:
##########
@@ -450,21 +451,23 @@ private CopyInResult insertGroupExpression(
      *
      * @param source source group
      * @param destination destination group
-     * @return merged group
      */
-    public Group mergeGroup(Group source, Group destination) {
+    public void mergeGroup(Group source, Group destination) {
         if (source.equals(destination)) {
-            return source;
+            return;
         }
         List<GroupExpression> needReplaceChild = Lists.newArrayList();
-        for (GroupExpression groupExpression : groupExpressions.values()) {
-            if (groupExpression.children().contains(source)) {
-                if (groupExpression.getOwnerGroup().equals(destination)) {
-                    // cycle, we should not merge
-                    return null;
-                }
-                needReplaceChild.add(groupExpression);
+        for (GroupExpression parent : source.getParentGroupExpressions()) {
+            if (parent.getOwnerGroup().equals(destination)) {

Review Comment:
   It's a good question, we need think about it in following PR.



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