From 70b2d0c58e1a85c9ecf7a22fb9382c7bd13f73fb Mon Sep 17 00:00:00 2001
From: Harvey Yue <yw_yuewei@126.com>
Date: Mon, 11 Nov 2024 20:26:09 +0800
Subject: [PATCH] [core] Fix merge schemas equal method issue (#4482)

---
 .../paimon/schema/SchemaMergingUtils.java     |  2 +-
 .../paimon/schema/SchemaMergingUtilsTest.java | 22 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/paimon-core/src/main/java/org/apache/paimon/schema/SchemaMergingUtils.java b/paimon-core/src/main/java/org/apache/paimon/schema/SchemaMergingUtils.java
index 30004b53fcfb..d7e21cd6562d 100644
--- a/paimon-core/src/main/java/org/apache/paimon/schema/SchemaMergingUtils.java
+++ b/paimon-core/src/main/java/org/apache/paimon/schema/SchemaMergingUtils.java
@@ -48,7 +48,7 @@ public static TableSchema mergeSchemas(
         AtomicInteger highestFieldId = new AtomicInteger(currentTableSchema.highestFieldId());
         RowType newRowType =
                 mergeSchemas(currentType, targetType, highestFieldId, allowExplicitCast);
-        if (newRowType == currentType) {
+        if (newRowType.equals(currentType)) {
             // It happens if the `targetType` only changes `nullability` but we always respect the
             // current's.
             return currentTableSchema;
diff --git a/paimon-core/src/test/java/org/apache/paimon/schema/SchemaMergingUtilsTest.java b/paimon-core/src/test/java/org/apache/paimon/schema/SchemaMergingUtilsTest.java
index 8ad40852721a..bfc6dd7aa36b 100644
--- a/paimon-core/src/test/java/org/apache/paimon/schema/SchemaMergingUtilsTest.java
+++ b/paimon-core/src/test/java/org/apache/paimon/schema/SchemaMergingUtilsTest.java
@@ -44,6 +44,7 @@
 import org.assertj.core.util.Lists;
 import org.junit.jupiter.api.Test;
 
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -92,6 +93,27 @@ public void testMergeTableSchemas() {
         assertThat(fields.get(4).type() instanceof RowType).isTrue();
     }
 
+    @Test
+    public void testMergeTableSchemaNotChanges() {
+        // Init the table schema
+        DataField a = new DataField(0, "a", new IntType());
+        DataField b = new DataField(1, "b", new DoubleType());
+        TableSchema current =
+                new TableSchema(
+                        0,
+                        Lists.newArrayList(a, b),
+                        3,
+                        new ArrayList<>(),
+                        Lists.newArrayList("a"),
+                        new HashMap<>(),
+                        "");
+
+        // fake the RowType of data with different field sequences
+        RowType t = new RowType(Lists.newArrayList(b, a));
+        TableSchema merged = SchemaMergingUtils.mergeSchemas(current, t, false);
+        assertThat(merged.id()).isEqualTo(0);
+    }
+
     @Test
     public void testMergeSchemas() {
         // This will test both `mergeSchemas` and `merge` methods.