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Merge pull request #24125 from taosdata/docs/szhou/tag-doc-restore 

docs: tag document restore
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12
docs/en/12-taos-sql/06-select.md
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@ -9,7 +9,7 @@ description: This document describes how to query data in TDengine.
```sql
SELECT {DATABASE() | CLIENT_VERSION() | SERVER_VERSION() | SERVER_STATUS() | NOW() | TODAY() | TIMEZONE() | CURRENT_USER() | USER() }
SELECT [hints] [DISTINCT] select_list
SELECT [hints] [DISTINCT] [TAGS] select_list
from_clause
[WHERE condition]
[partition_by_clause]
@ -182,7 +182,7 @@ The TBNAME pseudocolumn in a supertable contains the names of subtables within t
The following SQL statement returns all unique subtable names and locations within the meters supertable:
```mysql
SELECT DISTINCT TBNAME, location FROM meters;
SELECT TAGS TBNAME, location FROM meters;
```
Use the `INS_TAGS` system table in `INFORMATION_SCHEMA` to query the information for subtables in a supertable. For example, the following statement returns the name and tag values for each subtable in the `meters` supertable.
@ -227,6 +227,14 @@ The \_IROWTS pseudocolumn can only be used with INTERP function. This pseudocolu
select _irowts, interp(current) from meters range('2020-01-01 10:00:00', '2020-01-01 10:30:00') every(1s) fill(linear);
```
### TAGS Query
The TAGS keyword returns only tag columns from all child tables when only tag columns are specified. One row containing tag columns is returned for each child table.
```sql
SELECT TAGS tag_name [, tag_name ...] FROM stb_name
```
## Query Objects
`FROM` can be followed by a number of tables or super tables, or can be followed by a sub-query.

14
docs/zh/12-taos-sql/06-select.md
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@ -9,7 +9,7 @@ description: 查询数据的详细语法
```sql
SELECT {DATABASE() | CLIENT_VERSION() | SERVER_VERSION() | SERVER_STATUS() | NOW() | TODAY() | TIMEZONE() | CURRENT_USER() | USER() }
SELECT [hints] [DISTINCT] select_list
SELECT [hints] [DISTINCT] [TAGS] select_list
from_clause
[WHERE condition]
[partition_by_clause]
@ -162,6 +162,16 @@ SELECT DISTINCT col_name [, col_name ...] FROM tb_name;
:::
### 标签查询
当查询的列只有标签列时，`TAGS` 关键字可以指定返回所有子表的标签列。每个子表只返回一行标签列。
返回所有子表的标签列：
```sql
SELECT TAGS tag_name [, tag_name ...] FROM stb_name
```
### 结果集列名
`SELECT`子句中，如果不指定返回结果集合的列名，结果集列名称默认使用`SELECT`子句中的表达式名称作为列名称。此外，用户可使用`AS`来重命名返回结果集合中列的名称。例如：
@ -182,7 +192,7 @@ taos> SELECT ts, ts AS primary_key_ts FROM d1001;
获取一个超级表所有的子表名及相关的标签信息：
```mysql
SELECT DISTINCT TBNAME, location FROM meters;
SELECT TAGS TBNAME, location FROM meters;
```
建议用户使用 INFORMATION_SCHEMA 下的 INS_TAGS 系统表来查询超级表的子表标签信息，例如获取超级表 meters 所有的子表名和标签值：