From 86b8e95045a633c1d347df3f7ffe2933470b022e Mon Sep 17 00:00:00 2001
From: jakevin <jakevingoo@gmail.com>
Date: Mon, 17 Apr 2023 23:12:26 +0800
Subject: [PATCH] [fix](Nereids): when GroupExpr already exists, we need to
 remove ParentExpression (#18749)

---
 .../java/org/apache/doris/nereids/memo/GroupExpression.java    | 2 +-
 .../src/main/java/org/apache/doris/nereids/memo/Memo.java      | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/GroupExpression.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/GroupExpression.java
index 12e9816f8e..afa6d51f9b 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/GroupExpression.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/GroupExpression.java
@@ -182,7 +182,7 @@ public class GroupExpression {
      */
     public boolean isUnused() {
         if (isUnused) {
-            Preconditions.checkState(children.isEmpty() || ownerGroup == null);
+            Preconditions.checkState(children.isEmpty() && ownerGroup == null);
             return true;
         }
         Preconditions.checkState(ownerGroup != null);
diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/Memo.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/Memo.java
index 7a8d62338d..4ad1b118dc 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/Memo.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/memo/Memo.java
@@ -427,6 +427,9 @@ public class Memo {
             if (target != null && !target.getGroupId().equals(existedGroupExpression.getOwnerGroup().getGroupId())) {
                 mergeGroup(existedGroupExpression.getOwnerGroup(), target);
             }
+            // When we create a GroupExpression, we will add it into ParentExpression of childGroup.
+            // But if it already exists, we should remove it from ParentExpression of childGroup.
+            groupExpression.children().forEach(childGroup -> childGroup.removeParentExpression(groupExpression));
             return CopyInResult.of(false, existedGroupExpression);
         }
         if (target != null) {