[doc](alter table) add notes for modify column (#23720)

docs/en/docs/sql-manual/sql-reference/Data-Definition-Statements/Alter/ALTER-TABLE-COLUMN.md

@@ -198,6 +198,7 @@ Note: Whether you modify the key column or the value column, you need to declare
 ALTER TABLE example_db.my_table
 MODIFY COLUMN val1 VARCHAR(64) REPLACE DEFAULT "abc";
 ```
+Note: You can only modify the column's data type; other attributes of the column must remain unchanged.
 
 9. Reorder the columns in example_rollup_index (set the original column order as: k1,k2,k3,v1,v2)
 

docs/zh-CN/docs/sql-manual/sql-reference/Data-Definition-Statements/Alter/ALTER-TABLE-COLUMN.md

@@ -198,6 +198,7 @@ MODIFY COLUMN col1 BIGINT KEY DEFAULT "1" AFTER col2;
 ALTER TABLE example_db.my_table 
 MODIFY COLUMN val1 VARCHAR(64) REPLACE DEFAULT "abc";
 ```
+注意：只能修改列的类型，列的其他属性维持原样
 
 9. 重新排序 example_rollup_index 中的列（设原列顺序为：k1,k2,k3,v1,v2）