diff --git a/be/src/olap/memtable.cpp b/be/src/olap/memtable.cpp
index 690b47426a0fcb..f7d674eee43b87 100644
--- a/be/src/olap/memtable.cpp
+++ b/be/src/olap/memtable.cpp
@@ -69,20 +69,17 @@ MemTable::MemTable(int64_t tablet_id, std::shared_ptr<TabletSchema> tablet_schem
             _resource_ctx->memory_context()->mem_tracker()->write_tracker());
     SCOPED_CONSUME_MEM_TRACKER(_mem_tracker);
     _vec_row_comparator = std::make_shared<RowInBlockComparator>(_tablet_schema);
-    _num_columns = _tablet_schema->num_columns();
     if (partial_update_info != nullptr) {
         _partial_update_mode = partial_update_info->update_mode();
         if (_partial_update_mode == UniqueKeyUpdateModePB::UPDATE_FIXED_COLUMNS) {
-            _num_columns = partial_update_info->partial_update_input_columns.size();
             if (partial_update_info->is_schema_contains_auto_inc_column &&
                 !partial_update_info->is_input_columns_contains_auto_inc_column) {
                 _is_partial_update_and_auto_inc = true;
-                _num_columns += 1;
             }
         }
     }
-    // TODO: Support ZOrderComparator in the future
     _init_columns_offset_by_slot_descs(slot_descs, tuple_desc);
+    // TODO: Support ZOrderComparator in the future
     _row_in_blocks = std::make_unique<DorisVector<std::shared_ptr<RowInBlock>>>();
     _load_mem_limit = MemInfo::mem_limit() * config::load_process_max_memory_limit_percent / 100;
 }
@@ -101,6 +98,7 @@ void MemTable::_init_columns_offset_by_slot_descs(const std::vector<SlotDescript
     if (_is_partial_update_and_auto_inc) {
         _column_offset.emplace_back(_column_offset.size());
     }
+    _num_columns = _column_offset.size();
 }
 
 void MemTable::_init_agg_functions(const vectorized::Block* block) {
diff --git a/regression-test/data/nereids_p0/update/update_after_create_rollup.out b/regression-test/data/nereids_p0/update/update_after_create_rollup.out
new file mode 100644
index 00000000000000..89d8f0a064f1c5
--- /dev/null
+++ b/regression-test/data/nereids_p0/update/update_after_create_rollup.out
@@ -0,0 +1,11 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !sql_before --
+2000	2025-09-22	China	Shanghai
+2001	2025-09-22	USA	NewYork
+2002	2025-09-22	US	London
+
+-- !sql_after --
+2000	2025-09-22	CN	beijing
+2001	2025-09-22	China	Shenzhen
+2002	2025-09-22	US	London
+
diff --git a/regression-test/suites/nereids_p0/update/update_after_create_rollup.groovy b/regression-test/suites/nereids_p0/update/update_after_create_rollup.groovy
new file mode 100644
index 00000000000000..7c6aca2cea5cfd
--- /dev/null
+++ b/regression-test/suites/nereids_p0/update/update_after_create_rollup.groovy
@@ -0,0 +1,164 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// This test reproduces the bug where UPDATE SET nullable_col = NULL crashes
+// Bug: CHECK failed: index < data.size() in block.h:182
+// Root cause: _num_columns set from partial_update_input_columns.size() but actual input has fewer columns
+
+suite('update_after_create_rollup') {
+    sql 'drop table if exists mow_table'
+    sql '''
+       CREATE TABLE `mow_table` (
+        `user_id` bigint NOT NULL COMMENT "用户 ID",
+        `event_date` date NOT NULL COMMENT "事件日期",
+        `event_time` datetime NOT NULL COMMENT "事件时间",
+        `country` varchar(128) NULL DEFAULT "UNKNOWN",
+        `city` text NULL COMMENT "城市信息",
+        `age` int NULL DEFAULT "0" COMMENT "用户年龄",
+        `is_active` boolean NULL DEFAULT "TRUE" COMMENT "是否活跃",
+        `balance` decimal(18,2) NULL DEFAULT "0.00" COMMENT "账户余额",
+        `score` double NULL COMMENT "浮点分数",
+        `last_login` datetime(3) NULL DEFAULT CURRENT_TIMESTAMP(3) COMMENT "最后登录时间",
+        `last_ip` ipv4 NULL DEFAULT "0.0.0.0" COMMENT "最近一次登录 IP",
+        `ipv6_addr` ipv6 NULL COMMENT "IPv6 地址",
+        `json_data` json NULL COMMENT "扩展 JSON 信息",
+        `user_metadata` variant NULL COMMENT "存储用户自定义半结构化数据",
+        `seq_col` bigint NULL DEFAULT "0" COMMENT "顺序列，测试 sequence",
+        `auto_inc_col` bigint NOT NULL AUTO_INCREMENT(1) COMMENT "自增列，用于测试",
+        `create_time` datetime(6) NULL DEFAULT CURRENT_TIMESTAMP COMMENT "创建时间",
+        `update_time` datetime(6) NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT "更新时间",
+        `tags` array<varchar(32)> NULL,
+        `metadata` json NULL,
+        `status` int NULL DEFAULT "1",
+        `created_at` datetime NULL DEFAULT CURRENT_TIMESTAMP,
+        `optional_data` varchar(64) NULL,
+        `required_data` int NOT NULL DEFAULT "0",
+        `last_status` int NULL DEFAULT "0",
+        `col1` int NULL DEFAULT "0",
+        `col2` varchar(32) NULL,
+        `a_very_long_column_name_that_is_just_under_the_limit` int NULL,
+        `long_default` varchar(255) NULL DEFAULT "a_very_long_default_value_that_is_just_under_the_limit_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz",
+        `max_int` int NULL DEFAULT "2147483647",
+        `min_int` int NULL DEFAULT "-2147483648",
+        `high_precision` decimal(38,10) NULL DEFAULT "1234567890123456789012345678.1234567890",
+        `test_col` int NULL DEFAULT "0",
+        `consistency_check` int NULL DEFAULT "42",
+        INDEX idx_json_data_inverted (`user_metadata`) USING INVERTED
+        ) ENGINE=OLAP
+        UNIQUE KEY(`user_id`, `event_date`, `event_time`)
+        PARTITION BY RANGE(`event_date`)
+        (PARTITION p2015 VALUES [('2015-01-01'), ('2016-01-01')),
+        PARTITION p2016 VALUES [('2016-01-01'), ('2017-01-01')),
+        PARTITION p2017 VALUES [('2017-01-01'), ('2018-01-01')),
+        PARTITION p2018 VALUES [('2018-01-01'), ('2019-01-01')),
+        PARTITION p2019 VALUES [('2019-01-01'), ('2020-01-01')),
+        PARTITION p2020 VALUES [('2020-01-01'), ('2021-01-01')),
+        PARTITION p2021 VALUES [('2021-01-01'), ('2022-01-01')),
+        PARTITION p2022 VALUES [('2022-01-01'), ('2023-01-01')),
+        PARTITION p2023 VALUES [('2023-01-01'), ('2024-01-01')),
+        PARTITION p2024 VALUES [('2024-01-01'), ('2025-01-01')),
+        PARTITION p2025 VALUES [('2025-01-01'), ('2026-01-01')),
+        PARTITION p2026 VALUES [('2026-01-01'), ('2027-01-01')),
+        PARTITION p2027 VALUES [('2027-01-01'), ('2028-01-01')),
+        PARTITION p2028 VALUES [('2028-01-01'), ('2029-01-01')),
+        PARTITION p2029 VALUES [('2029-01-01'), ('2030-01-01')),
+        PARTITION p2030 VALUES [('2030-01-01'), ('2030-12-31')),
+        PARTITION p2031 VALUES [('2031-01-01'), ('2032-01-01')),
+        PARTITION p2032 VALUES [('2032-01-01'), ('2033-01-01')))
+        DISTRIBUTED BY HASH(`user_id`) BUCKETS 3
+        PROPERTIES (
+        "replication_allocation" = "tag.location.default: 1",
+        "min_load_replica_num" = "-1",
+        "bloom_filter_columns" = "country, city",
+        "is_being_synced" = "false",
+        "dynamic_partition.enable" = "true",
+        "dynamic_partition.time_unit" = "YEAR",
+        "dynamic_partition.time_zone" = "Asia/Shanghai",
+        "dynamic_partition.start" = "-10",
+        "dynamic_partition.end" = "7",
+        "dynamic_partition.prefix" = "p",
+        "dynamic_partition.replication_allocation" = "tag.location.default: 1",
+        "dynamic_partition.buckets" = "3",
+        "dynamic_partition.create_history_partition" = "false",
+        "dynamic_partition.history_partition_num" = "-1",
+        "dynamic_partition.hot_partition_num" = "0",
+        "dynamic_partition.reserved_history_periods" = "NULL",
+        "dynamic_partition.storage_policy" = "",
+        "storage_medium" = "hdd",
+        "storage_format" = "V2",
+        "inverted_index_storage_format" = "V3",
+        "enable_unique_key_merge_on_write" = "true",
+        "light_schema_change" = "true",
+        "disable_auto_compaction" = "false",
+        "enable_single_replica_compaction" = "false",
+        "group_commit_interval_ms" = "10000",
+        "group_commit_data_bytes" = "134217728",
+        "enable_mow_light_delete" = "false"
+        );
+    '''
+
+    sql '''
+        INSERT INTO mow_table(user_id,event_date,event_time,country,city) VALUES 
+        (2000,'2025-09-22','2025-09-22 10:00:00','China','Shanghai'),
+        (2001,'2025-09-22','2025-09-22 11:00:00','USA','NewYork'),
+        (2002,'2025-09-22','2025-09-22 12:00:00','US','London');
+    '''
+
+    qt_sql_before 'select user_id, event_date, country, city from mow_table order by user_id'
+
+    // Add a rollup that's missing the 'city' column
+    sql """
+        ALTER TABLE mow_table ADD ROLLUP rollup1(event_date, event_time, user_id, country, update_time)
+    """
+    sleep(10000)
+    explain {
+        sql('''
+            SELECT event_date, country, count(*) 
+            FROM mow_table 
+            WHERE event_date = '2025-09-22'
+            GROUP BY event_date, country
+        ''')
+        contains "rollup1"
+    }
+    
+    // Test 1: UPDATE column not in rollup1 (city)
+    sql 'UPDATE mow_table SET city = "beijing" WHERE user_id = 2000'
+    def result1 = sql 'SELECT city FROM mow_table WHERE user_id = 2000'
+    assertEquals(1, result1.size())
+    assertEquals('beijing', result1[0][0])
+    
+    // Test 2: UPDATE column in rollup1 (country)
+    sql 'UPDATE mow_table SET country = "CN" WHERE user_id = 2000'
+    def result2 = sql 'SELECT country FROM mow_table WHERE user_id = 2000'
+    assertEquals(1, result2.size())
+    assertEquals('CN', result2[0][0])
+
+    // Test 3: UPDATE both columns (one in rollup, one not)
+    sql 'UPDATE mow_table SET city = "Shenzhen", country = "China" WHERE user_id = 2001'
+    def result3 = sql 'SELECT city, country FROM mow_table WHERE user_id = 2001'
+    assertEquals(1, result3.size())
+    assertEquals('Shenzhen', result3[0][0])
+    assertEquals('China', result3[0][1])
+
+    qt_sql_after '''
+        SELECT user_id, event_date, country, city 
+        FROM mow_table 
+        ORDER BY user_id
+    '''
+
+    sql 'drop table if exists mow_table'
+}