refine modify column

[wjhuang2016]

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[qiancai]

add the do-not-merge/hold label as the change in this PR won't be included in v8.5.4

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[qiancai]

Suggested change

	> 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。
	> 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，以保持数据一致性。

[qiancai]

Suggested change

	从 v8.5.5 和 v9.0.0 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：
	从 v8.5.5 和 v9.0.0 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`），在进行以下类型变更时，TiDB 将不再进行表数据重建，只进行部分索引的重建：

[qiancai]

Suggested change

	Reorg-Data 指的是在修改列类型时，TiDB 需要对表中的现有数据进行重建，包括读取原数据，按照新的数据格式进行处理，然后重新写入表中。这类操作通常比较耗时，时间消耗与表中的数据量成正比。