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refine modify column #21110

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8 changes: 7 additions & 1 deletion sql-statements/sql-statement-modify-column.md
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Expand Up @@ -14,6 +14,12 @@ aliases: ['/docs-cn/dev/sql-statements/sql-statement-modify-column/','/docs-cn/d
- `DECIMAL` 精度修改
- 从 `VARCHAR(10)` 到 `VARCHAR(5)` 的长度压缩

从 v8.5.4 版本起，TiDB 优化了部分 Reorg-Data 类型变更的执行效率。在 [SQL 模式](/sql-mode.md)非严格模式（即 `sql_mode` 值包含 `STRICT_TRANS_TABLES` 或 `STRICT_ALL_TABLES`），以下类型变更将不再进行数据重建（Meta-Only 变更）：
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@joechenrh joechenrh Nov 25, 2025

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从 v8.5.4 版本起，TiDB 优化了部分 Reorg-Data 类型变更的执行效率。在 [SQL 模式](/sql-mode.md)非严格模式（即 `sql_mode` 值包含 `STRICT_TRANS_TABLES` 或 `STRICT_ALL_TABLES`），以下类型变更将不再进行数据重建（Meta-Only 变更）：
从 v8.5.4 版本起，TiDB 优化了部分 Reorg-Data 类型变更的执行效率。在 [SQL 模式](/sql-mode.md)严格模式（即 `sql_mode` 值包含 `STRICT_TRANS_TABLES` 或 `STRICT_ALL_TABLES`），以下类型变更将不再进行表数据重建，只进行部分索引的重建：

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@qiancai qiancai Nov 26, 2025 •
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Please update v8.5.4 to v8.5.5 if it is planned in v8.5.5

- 整数类型之间的变更（例如 `BIGINT` 到 `INT`）
- 字符串类型之间的变更（例如 `VARCHAR(200)` 到 `VARCHAR(100)`）

注意：VARCHAR 类型往 CHAR 类型变更时，要求所有的旧数据的尾部均不包含空格，否则需要进行 Reorg-Data。
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@qiancai qiancai Nov 25, 2025

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注意：VARCHAR 类型往 CHAR 类型变更时，要求所有的旧数据的尾部均不包含空格，否则需要进行 Reorg-Data。
> **注意：**
>
> 当 `VARCHAR` 转换为 `CHAR` 时，要求所有原数据的末尾均不包含空格；若不满足该条件，TiDB 仍会执行 Reorg-Data。


## 语法图

```ebnf+diagram
Expand Down Expand Up @@ -168,7 +174,7 @@ CREATE TABLE `t1` (
> ERROR 1406 (22001): Data Too Long, field len 4, data len 5
> ```
>
> - 由于和 Async Commit 功能兼容，DDL 在开始进入到 Reorg Data 前会有一定时间（约 2.5s）的等待处理：
> - 由于和 Async Commit 功能兼容, 在关闭元数据锁的情况下，DDL 在开始进入到 Reorg Data 前会有一定时间（约 2.5s）的等待处理：
>
> ```
> Query OK, 0 rows affected (2.52 sec)
Expand Down