[Doc] Resolve Historical Conflict Documents (#10997)

* Resolve Historical Conflict Documents

docs/en/docs/admin-manual/cluster-management/upgrade.md

@@ -86,3 +86,10 @@ Doris can upgrade smoothly by rolling upgrades. The following steps are recommen
 1. Confirm that the new version of the file is deployed. Restart FE and BE instances one by one.
 2. It is suggested that BE be restarted one by one and FE be restarted one by one. Because Doris usually guarantees backward compatibility between FE and BE, that is, the old version of FE can access the new version of BE. However, the old version of BE may not be supported to access the new version of FE.
 3. It is recommended to restart the next instance after confirming the previous instance started successfully. Refer to the Installation Deployment Document for the identification of successful instance startup.
+
+## About version rollback
+Because the database is a stateful service, Doris cannot support version rollback (version downgrade) in most cases. In some cases, the rollback of the 3-bit or 4-bit version can be supported, but the rollback of the 2-bit version will not be supported.
+
+Therefore, it is recommended to upgrade some nodes and observe the business operation (gray upgrade) to reduce the upgrade risk.
+
+**Illegal rollback operation may cause data loss and damage.** 

docs/en/docs/sql-manual/sql-functions/string-functions/substr.md

@@ -0,0 +1,50 @@
+---
+{
+"title": "substr",
+"language": "en"
+}
+---
+
+<!--
+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.
+-->
+
+## substr
+### Description
+#### Syntax
+
+`VARCHAR substr(VARCHAR content, INT start, INT length)`
+
+Find a substring, return the part of the string described by the first parameter starting from start and having a length of len. The index of the first letter is 1.
+
+### example
+
+```
+mysql> select substr("Hello doris", 2, 1);
++-----------------------------+
+| substr('Hello doris', 2, 1) |
++-----------------------------+
+| e                           |
++-----------------------------+
+mysql> select substr("Hello doris", 1, 2);
++-----------------------------+
+| substr('Hello doris', 1, 2) |
++-----------------------------+
+| He                          |
++-----------------------------+
+```
+### keywords
+SUBSTR

docs/zh-CN/docs/admin-manual/cluster-management/upgrade.md

@@ -86,3 +86,9 @@ Doris 可以通过滚动升级的方式，平滑进行升级。建议按照以
 1. 确认新版本的文件部署完成后。逐台重启 FE 和 BE 实例即可。
 2. 建议逐台重启 BE 后，再逐台重启 FE。因为通常 Doris 保证 FE 到 BE 的向后兼容性，即老版本的 FE 可以访问新版本的 BE。但可能不支持老版本的 BE 访问新版本的 FE。
 3. 建议确认前一个实例启动成功后，再重启下一个实例。实例启动成功的标识，请参阅安装部署文档。
+
+## 关于版本回滚
+因为数据库是一个有状态的服务，所以在大多数情况下，Doris 无法支持版本回滚（版本降级）。在某些情况下，可以支持 3 位或 4 位版本的回滚，但不会支持 2 位版本的回滚。
+所以建议通过先升级部分节点并观察业务运行情况的方式（灰度升级）来降低升级风险。
+
+**非法的回滚操作可能导致数据丢失和损坏。**

docs/zh-CN/docs/sql-manual/sql-functions/string-functions/substr.md

@@ -0,0 +1,50 @@
+---
+{
+"title": "substr",
+"language": "zh-CN"
+}
+---
+
+<!-- 
+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.
+-->
+
+## substr
+### description
+#### Syntax
+
+`VARCHAR substr(VARCHAR content, INT start, INT length)`
+
+求子字符串，返回第一个参数描述的字符串中从start开始长度为len的部分字符串。首字母的下标为1。
+
+### example
+
+```
+mysql> select substr("Hello doris", 2, 1);
++-----------------------------+
+| substr('Hello doris', 2, 1) |
++-----------------------------+
+| e                           |
++-----------------------------+
+mysql> select substr("Hello doris", 1, 2);
++-----------------------------+
+| substr('Hello doris', 1, 2) |
++-----------------------------+
+| He                          |
++-----------------------------+
+```
+### keywords
+SUBSTR