Fix broken link in shard-merge-best-practices.md and addd a missing section (#900) (#901)

Author: ti-chi-bot

en/shard-merge-best-practices.md

@@ -117,6 +117,10 @@ Then you can perform the following steps to fix the `ERROR 1062 (23000): Duplica
 
 3. Run `query-status` to verify whether the data migration task is successfully processed and whether the data from upstream has already been merged and migrated to the downstream database.
 
+## Special processing when the upstream RDS contains sharded tables
+
+If the upstream data source is an RDS and it contains sharded tables, the table names in MySQL binlog might be invisible when connecting to a SQL client. For example, if the upstream is a UCloud distributed database, the table name in the binlog might have an extra prefix `_0001`. Therefore, you need to configure [table routing](key-features.md#table-routing) based on the table names in binlog, instead of those in the SQL client.
+
 ## Create/drop tables in the upstream
 
 In [Merge and Migrate Data from Sharded Tables](feature-shard-merge-pessimistic.md#principles), it is clear that the coordination of sharding DDL lock depends on whether the downstream database receives the DDL statements of all upstream sharded tables. In addition, DM currently **does not support** dynamically creating or dropping sharded tables in the upstream. Therefore, to create or drop sharded tables in the upstream, it is recommended to perform the following steps.

zh/shard-merge-best-practices.md

@@ -69,11 +69,11 @@ CREATE TABLE `tbl_no_pk` (
     ```
 
 2. 在 `task.yaml` 文件中增加如下配置跳过自增主键冲突检查：
-    
+
     ```yaml
     ignore-checking-items: ["auto_increment_ID"]
     ```
-    
+
 3. 启动数据迁移任务，执行全量与增量数据迁移。
 
 4. 通过 `query-status` 验证数据迁移任务是否正常，在下游数据库中验证合表中是否已经存在了来自上游的数据。
@@ -116,7 +116,7 @@ CREATE TABLE `tbl_multi_pk` (
 
 ## 上游 RDS 封装分库分表的处理
 
-上游数据源为 RDS 且使用了其分库分表功能的情况下，MySQL binlog 中的表名在 SQL client 连接时可能并不可见。例如在 UCloud 分布式数据库 [UDDB](https://www.ucloud.cn/site/product/uddb.html) 中，其 binlog 表名可能会多出 `_0001` 的后缀。这需要根据 binlog 中的表名规律，而不是 SQL client 所见的表名，来配置 [table routing 规则](key-features.md#table-routing)。
+上游数据源为 RDS 且使用了其分库分表功能的情况下，MySQL binlog 中的表名在 SQL client 连接时可能并不可见。例如在 UCloud 分布式数据库 [UDDB](https://docs.ucloud.cn/uddb/README) 中，其 binlog 表名可能会多出 `_0001` 的后缀。这需要根据 binlog 中的表名规律，而不是 SQL client 所见的表名，来配置 [table routing 规则](key-features.md#table-routing)。
 
 ## 合表迁移过程中在上游增/删表