docs:[TS-5131] Modify description about backquote.

docs/en/12-taos-sql/06-select.md

@@ -459,7 +459,7 @@ SELECT ... FROM (SELECT ... FROM ...) ...;
 :::info
 
 - The result of a nested query is returned as a virtual table used by the outer query. It's recommended to give an alias to this table for the convenience of using it in the outer query.
-- Outer queries support directly referencing columns or pseudo-columns of inner queries in the form of column names or `column names`.
+- Outer queries support directly referencing columns or pseudo-columns of inner queries in the form of column names or \`column names\`.
 - JOIN operation is allowed between tables/STables inside both inner and outer queries. Join operation can be performed on the result set of the inner query.
 - The features that can be used in the inner query are the same as those that can be used in a non-nested query.
   - `ORDER BY` inside the inner query is unnecessary and will slow down the query performance significantly. It is best to avoid the use of `ORDER BY` inside the inner query.

docs/en/12-taos-sql/18-escape.md

@@ -18,7 +18,7 @@ description: This document describes the usage of escape characters in TDengine.
 
 ## Restrictions
 
-1. If there are escape characters in identifiers (database name, table name, column name)
+1. If there are escape characters in identifiers (database name, table name, column name, alias Name)
    - Identifier without ``: Error will be returned because identifier must be constituted of digits, ASCII characters or underscore and can't be started with digits
    - Identifier quoted with ``: Original content is kept, no escaping
 2. If there are escape characters in values

docs/zh/12-taos-sql/06-select.md

@@ -459,7 +459,7 @@ SELECT ... FROM (SELECT ... FROM ...) ...;
 :::info
 
 - 内层查询的返回结果将作为“虚拟表”供外层查询使用，此虚拟表建议起别名，以便于外层查询中方便引用。
-- 外层查询支持直接通过列名或`列名`的形式引用内层查询的列或伪列。
+- 外层查询支持直接通过列名或\`列名\`的形式引用内层查询的列或伪列。
 - 在内层和外层查询中，都支持普通的表间/超级表间 JOIN。内层查询的计算结果也可以再参与数据子表的 JOIN 操作。
 - 内层查询支持的功能特性与非嵌套的查询语句能力是一致的。
   - 内层查询的 ORDER BY 子句一般没有意义，建议避免这样的写法以免无谓的资源消耗。

docs/zh/12-taos-sql/18-escape.md

@@ -20,7 +20,7 @@ description: TDengine 中使用转义字符的详细规则
 
 ## 转义字符使用规则
 
-1. 标识符里有转义字符（数据库名、表名、列名）
+1. 标识符里有转义字符（数据库名、表名、列名、别名）
    1. 普通标识符： 直接提示错误的标识符，因为标识符规定必须是数字、字母和下划线，并且不能以数字开头。
    2. 反引号``标识符： 保持原样，不转义
 2. 数据里有转义字符