docs/zh/UserGuide/Query-Data/Result-Format.md

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# 查询结果集格式

在 IoTDB 中，查询结果集默认按照时间对齐，同时支持另外两种结果返回形式：

- 设备时间对齐 `align by device` 
- 时序不对齐 `disable align`

注意：对齐方式子句只能用于查询语句句尾。

## 按设备对齐

在 `align by device` 对齐方式下，设备名会单独作为一列出现。如果 select 子句中有 `n` 列，最终结果就会有该 `n + 2` 列（时间列和设备名字列）。

> 注意：
>
> 1.可以将 'align by device' 的结果看成一张关系表，`Time + Device` 看做其主键。
>
> 2.结果集首先按照 `Device` 进行排序,然后按照 `Time` 排序。

SQL 形如：

```sql
select * from root.ln.** where time <= 2017-11-01T00:01:00 align by device
```

结果如下：

```
+-----------------------------+-----------------+-----------+------+--------+
|                         Time|           Device|temperature|status|hardware|
+-----------------------------+-----------------+-----------+------+--------+
|2017-11-01T00:00:00.000+08:00|root.ln.wf01.wt01|      25.96|  true|    null|
|2017-11-01T00:01:00.000+08:00|root.ln.wf01.wt01|      24.36|  true|    null|
|1970-01-01T08:00:00.001+08:00|root.ln.wf02.wt02|       null|  true|      v1|
|1970-01-01T08:00:00.002+08:00|root.ln.wf02.wt02|       null| false|      v2|
|2017-11-01T00:00:00.000+08:00|root.ln.wf02.wt02|       null|  true|      v2|
|2017-11-01T00:01:00.000+08:00|root.ln.wf02.wt02|       null|  true|      v2|
+-----------------------------+-----------------+-----------+------+--------+
Total line number = 6
It costs 0.012s
```

## 时序不对齐

在 `disable align` 对齐方式下，如果 select 子句中有 `n` 列，最终结果就会有该 `n * 2` 列（时间序列的时间和值）。

注：时序不对齐方式不能用于聚合查询、空值填充，但可使用 Limit 和 Offset 语句进行分页。

SQL 形如：

```sql
select * from root.ln.** where time <= 2017-11-01T00:01:00 disable align
```

结果如下：

```
+-----------------------------+--------------------------+-----------------------------+------------------------+-----------------------------+-----------------------------+-----------------------------+------------------------+
|                         Time|root.ln.wf02.wt02.hardware|                         Time|root.ln.wf02.wt02.status|                         Time|root.ln.wf01.wt01.temperature|                         Time|root.ln.wf01.wt01.status|
+-----------------------------+--------------------------+-----------------------------+------------------------+-----------------------------+-----------------------------+-----------------------------+------------------------+
|1970-01-01T08:00:00.001+08:00|                        v1|1970-01-01T08:00:00.001+08:00|                    true|2017-11-01T00:00:00.000+08:00|                        25.96|2017-11-01T00:00:00.000+08:00|                    true|
|1970-01-01T08:00:00.002+08:00|                        v2|1970-01-01T08:00:00.002+08:00|                   false|2017-11-01T00:01:00.000+08:00|                        24.36|2017-11-01T00:01:00.000+08:00|                    true|
|2017-11-01T00:00:00.000+08:00|                        v2|2017-11-01T00:00:00.000+08:00|                    true|                         null|                         null|                         null|                    null|
|2017-11-01T00:01:00.000+08:00|                        v2|2017-11-01T00:01:00.000+08:00|                    true|                         null|                         null|                         null|                    null|
+-----------------------------+--------------------------+-----------------------------+------------------------+-----------------------------+-----------------------------+-----------------------------+------------------------+
Total line number = 4
It costs 0.018s
```