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# 节点管理

## 查看子路径

```
SHOW CHILD PATHS pathPattern
```

可以查看此路径模式所匹配的所有路径的下一层的所有路径，即pathPattern.*所匹配的路径。

示例：

* 查询 root.ln 的下一层：show child paths root.ln

```
+------------+
| child paths|
+------------+
|root.ln.wf01|
|root.ln.wf02|
+------------+
```

* 查询形如 root.xx.xx.xx 的路径：show child paths root.\*.\*

```
+---------------+
|    child paths|
+---------------+
|root.ln.wf01.s1|
|root.ln.wf02.s2|
+---------------+
```

## 查看子节点

```
SHOW CHILD NODES pathPattern
```

可以查看此路径模式所匹配的节点的下一层的所有节点。

示例：

* 查询 root 的下一层：show child nodes root

```
+------------+
| child nodes|
+------------+
|          ln|
+------------+
```

* 查询 root.ln 的下一层 ：show child nodes root.ln

```
+------------+
| child nodes|
+------------+
|        wf01|
|        wf02|
+------------+
```

## 统计节点数

IoTDB 支持使用`COUNT NODES <PathPattern> LEVEL=<INTEGER>`来统计当前 Metadata
 树下满足某路径模式的路径中指定层级的节点个数。这条语句可以用来统计带有特定采样点的设备数。例如：

```
IoTDB > COUNT NODES root.** LEVEL=2
IoTDB > COUNT NODES root.ln.** LEVEL=2
IoTDB > COUNT NODES root.ln.wf01.* LEVEL=3
IoTDB > COUNT NODES root.**.temperature LEVEL=3
```

对于上面提到的例子和 Metadata Tree，你可以获得如下结果：

```
+-----+
|count|
+-----+
|    4|
+-----+
Total line number = 1
It costs 0.003s

+-----+
|count|
+-----+
|    2|
+-----+
Total line number = 1
It costs 0.002s

+-----+
|count|
+-----+
|    1|
+-----+
Total line number = 1
It costs 0.002s

+-----+
|count|
+-----+
|    2|
+-----+
Total line number = 1
It costs 0.002s
```

> 注意：时间序列的路径只是过滤条件，与 level 的定义无关。

## 查看设备

* SHOW DEVICES pathPattern? (WITH STORAGE GROUP)? limitClause? #showDevices

与 `Show Timeseries` 相似，IoTDB 目前也支持两种方式查看设备。

* `SHOW DEVICES` 语句显示当前所有的设备信息，等价于 `SHOW DEVICES root.**`。
* `SHOW DEVICES <PathPattern>` 语句规定了 `PathPattern`，返回给定的路径模式所匹配的设备信息。

SQL 语句如下所示：

```
IoTDB> show devices
IoTDB> show devices root.ln.**
```

你可以获得如下数据：

```
+-------------------+---------+
|            devices|isAligned|
+-------------------+---------+
|  root.ln.wf01.wt01|    false|
|  root.ln.wf02.wt02|    false|
|root.sgcc.wf03.wt01|    false|
|    root.turbine.d1|    false|
+-------------------+---------+
Total line number = 4
It costs 0.002s

+-----------------+---------+
|          devices|isAligned|
+-----------------+---------+
|root.ln.wf01.wt01|    false|
|root.ln.wf02.wt02|    false|
+-----------------+---------+
Total line number = 2
It costs 0.001s
```

其中，`isAligned`表示该设备下的时间序列是否对齐。

查看设备及其存储组信息，可以使用 `SHOW DEVICES WITH STORAGE GROUP` 语句。

* `SHOW DEVICES WITH STORAGE GROUP` 语句显示当前所有的设备信息和其所在的存储组，等价于 `SHOW DEVICES root.**`。
* `SHOW DEVICES <PathPattern> WITH STORAGE GROUP` 语句规定了 `PathPattern`，返回给定的路径模式所匹配的设备信息和其所在的存储组。

SQL 语句如下所示：

```
IoTDB> show devices with storage group
IoTDB> show devices root.ln.** with storage group
```

你可以获得如下数据：

```
+-------------------+-------------+---------+
|            devices|storage group|isAligned|
+-------------------+-------------+---------+
|  root.ln.wf01.wt01|      root.ln|    false|
|  root.ln.wf02.wt02|      root.ln|    false|
|root.sgcc.wf03.wt01|    root.sgcc|    false|
|    root.turbine.d1| root.turbine|    false|
+-------------------+-------------+---------+
Total line number = 4
It costs 0.003s

+-----------------+-------------+---------+
|          devices|storage group|isAligned|
+-----------------+-------------+---------+
|root.ln.wf01.wt01|      root.ln|    false|
|root.ln.wf02.wt02|      root.ln|    false|
+-----------------+-------------+---------+
Total line number = 2
It costs 0.001s
```

## 统计设备数量

* COUNT DEVICES <PathPattern>

上述语句用于统计设备的数量，同时允许指定`PathPattern` 用于统计匹配该`PathPattern` 的设备数量

SQL 语句如下所示：

```
IoTDB> show devices
IoTDB> count devices
IoTDB> count devices root.ln.**
```

你可以获得如下数据：

```
+-------------------+---------+
|            devices|isAligned|
+-------------------+---------+
|root.sgcc.wf03.wt03|    false|
|    root.turbine.d1|    false|
|  root.ln.wf02.wt02|    false|
|  root.ln.wf01.wt01|    false|
+-------------------+---------+
Total line number = 4
It costs 0.024s

+-------+
|devices|
+-------+
|      4|
+-------+
Total line number = 1
It costs 0.004s

+-------+
|devices|
+-------+
|      2|
+-------+
Total line number = 1
It costs 0.004s
```
