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    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav>  <ul class="sidebar-links"><li><section class="sidebar-group depth-0"><p class="sidebar-heading"><span>IoTDB User Guide (In progress)</span> <!----></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Get Started</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Overview</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Concept</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Server</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Client</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>Operation Manual</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/UserGuide/Master/Operation Manual/DDL Data Definition Language.html" class="active sidebar-link">DDL (Data Definition Language)</a></li><li><a href="/UserGuide/Master/Operation Manual/DML Data Manipulation Language.html" class="sidebar-link">DML (Data Manipulation Language)</a></li><li><a href="/UserGuide/Master/Operation Manual/Administration.html" class="sidebar-link">Administration</a></li><li><a href="/UserGuide/Master/Operation Manual/SQL Reference.html" class="sidebar-link">SQL Reference</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>System Tools</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Ecosystem Integration</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Architecture</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Comparison with TSDBs</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="content content__default"><h1 id="ddl-data-definition-language"><a href="#ddl-data-definition-language" class="header-anchor">#</a> DDL (Data Definition Language)</h1> <h2 id="create-storage-group"><a href="#create-storage-group" class="header-anchor">#</a> Create Storage Group</h2> <p>According to the storage model we can set up the corresponding storage group. The SQL statements for creating storage groups are as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB &gt; set storage group to root.ln
IoTDB &gt; set storage group to root.sgcc
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>We can thus create two storage groups using the above two SQL statements.</p> <p>It is worth noting that when the path itself or the parent/child layer of the path is already set as a storage group, the path is then not allowed to be set as a storage group. For example, it is not feasible to set <code>root.ln.wf01</code> as a storage group when two storage groups <code>root.ln</code> and <code>root.sgcc</code> exist. The system gives the corresponding error prompt as shown below:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; set storage group to root.ln.wf01
Msg: org.apache.iotdb.exception.MetadataException: org.apache.iotdb.exception.MetadataException: The prefix of root.ln.wf01 has been set to the storage group.
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h2 id="show-storage-group"><a href="#show-storage-group" class="header-anchor">#</a> Show Storage Group</h2> <p>After creating the storage group, we can use the <a href="/UserGuide/Master/Operation Manual/SQL Reference.html">SHOW STORAGE GROUP</a> statement and <a href="/UserGuide/Master/Operation Manual/SQL Reference.html">SHOW STORAGE GROUP &lt;PrefixPath&gt;</a> to view the storage groups. The SQL statements are as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; show storage group
IoTDB&gt; show storage group root.ln
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>The result is as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>+-------------+
|storage group|
+-------------+
|    root.sgcc|
|      root.ln|
+-------------+
Total line number = 2
It costs 0.060s
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><h2 id="delete-storage-group"><a href="#delete-storage-group" class="header-anchor">#</a> Delete Storage Group</h2> <p>User can use the <code>DELETE STORAGE GROUP &lt;PrefixPath&gt;</code> statement to delete all storage groups under the prefixPath. Please note the data in the storage group will also be deleted.</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB &gt; DELETE STORAGE GROUP root.ln
IoTDB &gt; DELETE STORAGE GROUP root.sgcc
// delete all data, all timeseries and all storage groups
IoTDB &gt; DELETE STORAGE GROUP root.*
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><h2 id="create-timeseries"><a href="#create-timeseries" class="header-anchor">#</a> Create Timeseries</h2> <p>According to the storage model selected before, we can create corresponding timeseries in the two storage groups respectively. The SQL statements for creating timeseries are as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB &gt; create timeseries root.ln.wf01.wt01.status with datatype=BOOLEAN,encoding=PLAIN
IoTDB &gt; create timeseries root.ln.wf01.wt01.temperature with datatype=FLOAT,encoding=RLE
IoTDB &gt; create timeseries root.ln.wf02.wt02.hardware with datatype=TEXT,encoding=PLAIN
IoTDB &gt; create timeseries root.ln.wf02.wt02.status with datatype=BOOLEAN,encoding=PLAIN
IoTDB &gt; create timeseries root.sgcc.wf03.wt01.status with datatype=BOOLEAN,encoding=PLAIN
IoTDB &gt; create timeseries root.sgcc.wf03.wt01.temperature with datatype=FLOAT,encoding=RLE
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>Notice that when in the CRATE TIMESERIES statement the encoding method conflicts with the data type, the system gives the corresponding error prompt as shown below:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; create timeseries root.ln.wf02.wt02.status WITH DATATYPE=BOOLEAN, ENCODING=TS_2DIFF
error: encoding TS_2DIFF does not support BOOLEAN
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>Please refer to <a href="/UserGuide/Master/Concept/Encoding.html">Encoding</a> for correspondence between data type and encoding.</p> <h3 id="tag-and-attribute-management"><a href="#tag-and-attribute-management" class="header-anchor">#</a> Tag and attribute management</h3> <p>We can also add an alias, extra tag and attribute information while creating one timeseries.
The SQL statements for creating timeseries with extra tag and attribute information are extended as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>create timeseries root.turbine.d1.s1(temprature) with datatype=FLOAT, encoding=RLE, compression=SNAPPY tags(tag1=v1, tag2=v2) attributes(attr1=v1, attr2=v2)
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>The <code>temprature</code> in the brackets is an alias for the sensor <code>s1</code>. So we can use <code>temprature</code> to replace <code>s1</code> anywhere.</p> <blockquote><p>IoTDB also supports <a href="/UserGuide/Master/Operation Manual/DML Data Manipulation Language.html">using AS function</a> to set alias. The difference between the two is: the alias set by the AS function is used to replace the whole time series name, temporary and not bound with the time series; while the alias mentioned above is only used as the alias of the sensor, which is bound with it and can be used equivalent to the original sensor name.</p></blockquote> <p>The only difference between tag and attribute is that we will maintain an inverted index on the tag, so we can use tag property in the show timeseries where clause which you can see in the following <code>Show Timeseries</code> section.</p> <blockquote><p>Notice that the size of the extra tag and attribute information shouldn't exceed the <code>tag_attribute_total_size</code>.</p></blockquote> <h2 id="update-tag-operation"><a href="#update-tag-operation" class="header-anchor">#</a> UPDATE TAG OPERATION</h2> <p>We can update the tag information after creating it as following:</p> <ul><li>Rename the tag/attribute key</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>ALTER timeseries root.turbine.d1.s1 RENAME tag1 TO newTag1
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>reset the tag/attribute value</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>ALTER timeseries root.turbine.d1.s1 SET newTag1=newV1, attr1=newV1
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>delete the existing tag/attribute</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>ALTER timeseries root.turbine.d1.s1 DROP tag1, tag2
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>add new tags</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>ALTER timeseries root.turbine.d1.s1 ADD TAGS tag3=v3, tag4=v4
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>add new attributes</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>ALTER timeseries root.turbine.d1.s1 ADD ATTRIBUTES attr3=v3, attr4=v4
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>upsert alias, tags and attributes</li></ul> <blockquote><p>add alias or a new key-value if the alias or key doesn't exist, otherwise, update the old one with new value.</p></blockquote> <div class="language- line-numbers-mode"><pre class="language-text"><code>ALTER timeseries root.turbine.d1.s1 UPSERT ALIAS=newAlias TAGS(tag3=v3, tag4=v4) ATTRIBUTES(attr3=v3, attr4=v4)
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h2 id="show-timeseries"><a href="#show-timeseries" class="header-anchor">#</a> Show Timeseries</h2> <ul><li><p>SHOW LATEST? TIMESERIES prefixPath? showWhereClause? limitClause?</p> <p>There are four optional clauses added in SHOW TIMESERIES, return information of time series</p></li></ul> <p>Timeseries information includes: timeseries path, alias of measurement, storage group it belongs to, data type, encoding type, compression type, tags and attributes.</p> <p>Examples:</p> <ul><li><p>SHOW TIMESERIES</p> <p>presents all timeseries information in JSON form</p></li> <li><p>SHOW TIMESERIES &lt;<code>Path</code>&gt;</p> <p>returns all timeseries information under the given &lt;<code>Path</code>&gt;.  &lt;<code>Path</code>&gt; needs to be a prefix path or a path with star or a timeseries path. SQL statements are as follows:</p></li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; show timeseries root
IoTDB&gt; show timeseries root.ln
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>The results are shown below respectively:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>+-------------------------------+--------+-------------+--------+--------+-----------+-------------------------------------------+--------------------------------------------------------+
|                     timeseries|   alias|storage group|dataType|encoding|compression|                                       tags|                                              attributes|
+-------------------------------+--------+-------------+--------+--------+-----------+-------------------------------------------+--------------------------------------------------------+
|root.sgcc.wf03.wt01.temperature|    null|    root.sgcc|   FLOAT|     RLE|     SNAPPY|                                       null|                                                    null|
|     root.sgcc.wf03.wt01.status|    null|    root.sgcc| BOOLEAN|   PLAIN|     SNAPPY|                                       null|                                                    null|
|             root.turbine.d1.s1|newAlias| root.turbine|   FLOAT|     RLE|     SNAPPY|{&quot;newTag1&quot;:&quot;newV1&quot;,&quot;tag4&quot;:&quot;v4&quot;,&quot;tag3&quot;:&quot;v3&quot;}|{&quot;attr2&quot;:&quot;v2&quot;,&quot;attr1&quot;:&quot;newV1&quot;,&quot;attr4&quot;:&quot;v4&quot;,&quot;attr3&quot;:&quot;v3&quot;}|
|     root.ln.wf02.wt02.hardware|    null|      root.ln|    TEXT|   PLAIN|     SNAPPY|                                       null|                                                    null|
|       root.ln.wf02.wt02.status|    null|      root.ln| BOOLEAN|   PLAIN|     SNAPPY|                                       null|                                                    null|
|  root.ln.wf01.wt01.temperature|    null|      root.ln|   FLOAT|     RLE|     SNAPPY|                                       null|                                                    null|
|       root.ln.wf01.wt01.status|    null|      root.ln| BOOLEAN|   PLAIN|     SNAPPY|                                       null|                                                    null|
+-------------------------------+--------+-------------+--------+--------+-----------+-------------------------------------------+--------------------------------------------------------+
Total line number = 7
It costs 0.016s

+-----------------------------+-----+-------------+--------+--------+-----------+----+----------+
|                   timeseries|alias|storage group|dataType|encoding|compression|tags|attributes|
+-----------------------------+-----+-------------+--------+--------+-----------+----+----------+
|   root.ln.wf02.wt02.hardware| null|      root.ln|    TEXT|   PLAIN|     SNAPPY|null|      null|
|     root.ln.wf02.wt02.status| null|      root.ln| BOOLEAN|   PLAIN|     SNAPPY|null|      null|
|root.ln.wf01.wt01.temperature| null|      root.ln|   FLOAT|     RLE|     SNAPPY|null|      null|
|     root.ln.wf01.wt01.status| null|      root.ln| BOOLEAN|   PLAIN|     SNAPPY|null|      null|
+-----------------------------+-----+-------------+--------+--------+-----------+----+----------+
Total line number = 4
It costs 0.004s
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br></div></div><ul><li><p>SHOW TIMESERIES (&lt;<code>PrefixPath</code>&gt;)? WhereClause</p> <p>returns all the timeseries information that satisfy the where condition and start with the prefixPath SQL statements are as follows:</p></li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>ALTER timeseries root.ln.wf02.wt02.hardware ADD TAGS unit=c
ALTER timeseries root.ln.wf02.wt02.status ADD TAGS description=test1
show timeseries root.ln where unit=c
show timeseries root.ln where description contains 'test1'
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>The results are shown below respectly:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>+--------------------------+-----+-------------+--------+--------+-----------+------------+----------+
|                timeseries|alias|storage group|dataType|encoding|compression|        tags|attributes|
+--------------------------+-----+-------------+--------+--------+-----------+------------+----------+
|root.ln.wf02.wt02.hardware| null|      root.ln|    TEXT|   PLAIN|     SNAPPY|{&quot;unit&quot;:&quot;c&quot;}|      null|
+--------------------------+-----+-------------+--------+--------+-----------+------------+----------+
Total line number = 1
It costs 0.005s

+------------------------+-----+-------------+--------+--------+-----------+-----------------------+----------+
|              timeseries|alias|storage group|dataType|encoding|compression|                   tags|attributes|
+------------------------+-----+-------------+--------+--------+-----------+-----------------------+----------+
|root.ln.wf02.wt02.status| null|      root.ln| BOOLEAN|   PLAIN|     SNAPPY|{&quot;description&quot;:&quot;test1&quot;}|      null|
+------------------------+-----+-------------+--------+--------+-----------+-----------------------+----------+
Total line number = 1
It costs 0.004s
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><blockquote><p>Notice that, we only support one condition in the where clause. Either it's an equal filter or it is an <code>contains</code> filter. In both case, the property in the where condition must be a tag.</p></blockquote> <ul><li><p>SHOW TIMESERIES LIMIT INT OFFSET INT</p> <p>returns all the timeseries information start from the offset and limit the number of series returned</p></li> <li><p>SHOW LATEST TIMESERIES</p> <p>all the returned timeseries information should be sorted in descending order of the last timestamp of timeseries</p></li></ul> <p>It is worth noting that when the queried path does not exist, the system will return no timeseries.</p> <h2 id="show-child-paths"><a href="#show-child-paths" class="header-anchor">#</a> Show Child Paths</h2> <div class="language- line-numbers-mode"><pre class="language-text"><code>SHOW CHILD PATHS prefixPath
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>Return all child paths of the prefixPath, the prefixPath could contains *.</p> <p>Example：</p> <ul><li>return the child paths of root.ln：show child paths root.ln</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>+------------+
| child paths|
+------------+
|root.ln.wf01|
|root.ln.wf02|
+------------+
Total line number = 2
It costs 0.002s
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><blockquote><p>get all paths in form of root.xx.xx.xx：show child paths root.xx.xx</p></blockquote> <h2 id="count-timeseries"><a href="#count-timeseries" class="header-anchor">#</a> Count Timeseries</h2> <p>IoTDB is able to use <code>COUNT TIMESERIES &lt;Path&gt;</code> to count the number of timeseries in the path. SQL statements are as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB &gt; COUNT TIMESERIES root
IoTDB &gt; COUNT TIMESERIES root.ln
IoTDB &gt; COUNT TIMESERIES root.ln.*.*.status
IoTDB &gt; COUNT TIMESERIES root.ln.wf01.wt01.status
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>Besides, <code>LEVEL</code> could be defined to show count the number of timeseries of each node at the given level in current Metadata Tree. This could be used to query the number of sensors under each device. The grammar is: <code>COUNT TIMESERIES &lt;Path&gt; GROUP BY LEVEL=&lt;INTEGER&gt;</code>.</p> <p>For example, if there are several timeseries (use <code>show timeseries</code> to show all timeseries):</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>+-------------------------------+--------+-------------+--------+--------+-----------+-------------------------------------------+--------------------------------------------------------+
|                     timeseries|   alias|storage group|dataType|encoding|compression|                                       tags|                                              attributes|
+-------------------------------+--------+-------------+--------+--------+-----------+-------------------------------------------+--------------------------------------------------------+
|root.sgcc.wf03.wt01.temperature|    null|    root.sgcc|   FLOAT|     RLE|     SNAPPY|                                       null|                                                    null|
|     root.sgcc.wf03.wt01.status|    null|    root.sgcc| BOOLEAN|   PLAIN|     SNAPPY|                                       null|                                                    null|
|             root.turbine.d1.s1|newAlias| root.turbine|   FLOAT|     RLE|     SNAPPY|{&quot;newTag1&quot;:&quot;newV1&quot;,&quot;tag4&quot;:&quot;v4&quot;,&quot;tag3&quot;:&quot;v3&quot;}|{&quot;attr2&quot;:&quot;v2&quot;,&quot;attr1&quot;:&quot;newV1&quot;,&quot;attr4&quot;:&quot;v4&quot;,&quot;attr3&quot;:&quot;v3&quot;}|
|     root.ln.wf02.wt02.hardware|    null|      root.ln|    TEXT|   PLAIN|     SNAPPY|                               {&quot;unit&quot;:&quot;c&quot;}|                                                    null|
|       root.ln.wf02.wt02.status|    null|      root.ln| BOOLEAN|   PLAIN|     SNAPPY|                    {&quot;description&quot;:&quot;test1&quot;}|                                                    null|
|  root.ln.wf01.wt01.temperature|    null|      root.ln|   FLOAT|     RLE|     SNAPPY|                                       null|                                                    null|
|       root.ln.wf01.wt01.status|    null|      root.ln| BOOLEAN|   PLAIN|     SNAPPY|                                       null|                                                    null|
+-------------------------------+--------+-------------+--------+--------+-----------+-------------------------------------------+--------------------------------------------------------+
Total line number = 7
It costs 0.004s
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>Then the Metadata Tree will be as below:</p> <center><img src="https://user-images.githubusercontent.com/19167280/69792176-1718f400-1201-11ea-861a-1a83c07ca144.jpg" style="width:100%;max-width:600px;margin-left:auto;margin-right:auto;display:block;"></center> <p>As can be seen, <code>root</code> is considered as <code>LEVEL=0</code>. So when you enter statements such as:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB &gt; COUNT TIMESERIES root GROUP BY LEVEL=1
IoTDB &gt; COUNT TIMESERIES root.ln GROUP BY LEVEL=2
IoTDB &gt; COUNT TIMESERIES root.ln.wf01 GROUP BY LEVEL=2
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>You will get following results:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>+------------+-----+
|      column|count|
+------------+-----+
|   root.sgcc|    2|
|root.turbine|    1|
|     root.ln|    4|
+------------+-----+
Total line number = 3
It costs 0.002s

+------------+-----+
|      column|count|
+------------+-----+
|root.ln.wf02|    2|
|root.ln.wf01|    2|
+------------+-----+
Total line number = 2
It costs 0.002s

+------------+-----+
|      column|count|
+------------+-----+
|root.ln.wf01|    2|
+------------+-----+
Total line number = 1
It costs 0.002s
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br></div></div><blockquote><p>Note: The path of timeseries is just a filter condition, which has no relationship with the definition of level.</p></blockquote> <h2 id="count-nodes"><a href="#count-nodes" class="header-anchor">#</a> Count Nodes</h2> <p>IoTDB is able to use <code>COUNT NODES &lt;PrefixPath&gt; LEVEL=&lt;INTEGER&gt;</code> to count the number of nodes at the given level in current Metadata Tree. This could be used to query the number of devices. The usage are as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB &gt; COUNT NODES root LEVEL=2
IoTDB &gt; COUNT NODES root.ln LEVEL=2
IoTDB &gt; COUNT NODES root.ln.wf01 LEVEL=3
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>As for the above mentioned example and Metadata tree, you can get following results:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>+-----+
|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
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br></div></div><blockquote><p>Note: The path of timeseries is just a filter condition, which has no relationship with the definition of level.
<code>PrefixPath</code> could contains <code>*</code>, but all nodes after <code>*</code> would be ignored. Only the prefix path before <code>*</code> is valid.</p></blockquote> <h2 id="delete-timeseries"><a href="#delete-timeseries" class="header-anchor">#</a> Delete Timeseries</h2> <p>To delete the timeseries we created before, we are able to use <code>DELETE TimeSeries &lt;PrefixPath&gt;</code> statement.</p> <p>The usage are as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; delete timeseries root.ln.wf01.wt01.status
IoTDB&gt; delete timeseries root.ln.wf01.wt01.temperature, root.ln.wf02.wt02.hardware
IoTDB&gt; delete timeseries root.ln.wf02.*
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h2 id="show-devices"><a href="#show-devices" class="header-anchor">#</a> Show Devices</h2> <p>Similar to <code>Show Timeseries</code>, IoTDB also supports two ways of viewing devices:</p> <ul><li><code>SHOW DEVICES</code> statement presents all devices information, which is equal to <code>SHOW DEVICES root</code>.</li> <li><code>SHOW DEVICES &lt;PrefixPath&gt;</code> statement specifies the <code>PrefixPath</code> and returns the devices information under the given level.</li></ul> <p>SQL statement is as follows:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; show devices
IoTDB&gt; show devices root.ln
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>You can get results below:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>+-------------------+
|            devices|
+-------------------+
|  root.ln.wf01.wt01|
|  root.ln.wf02.wt02|
|root.sgcc.wf03.wt01|
|    root.turbine.d1|
+-------------------+
Total line number = 4
It costs 0.002s

+-----------------+
|          devices|
+-----------------+
|root.ln.wf01.wt01|
|root.ln.wf02.wt02|
+-----------------+
Total line number = 2
It costs 0.001s
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br></div></div><h1 id="ttl"><a href="#ttl" class="header-anchor">#</a> TTL</h1> <p>IoTDB supports storage-level TTL settings, which means it is able to delete old data automatically and periodically. The benefit of using TTL is that hopefully you can control the total disk space usage and prevent the machine from running out of disks. Moreover, the query performance may downgrade as the total number of files goes up and the memory usage also increase as there are more files. Timely removing such files helps to keep at a high query performance level and reduce memory usage.</p> <h2 id="set-ttl"><a href="#set-ttl" class="header-anchor">#</a> Set TTL</h2> <p>The SQL Statement for setting TTL is as follow:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; set ttl to root.ln 3600000
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>This example means that for data in <code>root.ln</code>, only that of the latest 1 hour will remain, the older one is removed or made invisible.</p> <h2 id="unset-ttl"><a href="#unset-ttl" class="header-anchor">#</a> Unset TTL</h2> <p>To unset TTL, we can use follwing SQL statement:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; unset ttl to root.ln
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>After unset TTL, all data will be accepted in <code>root.ln</code></p> <h2 id="show-ttl"><a href="#show-ttl" class="header-anchor">#</a> Show TTL</h2> <p>To Show TTL, we can use following SQL statement:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; SHOW ALL TTL
IoTDB&gt; SHOW TTL ON StorageGroupNames
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>The SHOW ALL TTL example gives the TTL for all storage groups.
The SHOW TTL ON  root.group1 , root.group2 , root.group3 example shows the TTL for the three storage
groups specified.
Note: the TTL for storage groups that do not have a TTL set will display as null.</p> <h2 id="flush"><a href="#flush" class="header-anchor">#</a> FLUSH</h2> <p>Persist all the data points in the memory table of the storage group to the disk, and seal the data file.</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; FLUSH 
IoTDB&gt; FLUSH root.ln
IoTDB&gt; FLUSH root.sg1,root.sg2
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h2 id="merge"><a href="#merge" class="header-anchor">#</a> MERGE</h2> <p>Merge sequence and unsequence data. Currently IoTDB supports the following two types of SQL to manually trigger the merge process of data files:</p> <ul><li><code>MERGE</code> Only rewrite overlapped Chunks, the merge speed is quick, while there will be redundant data on the disk eventually.</li> <li><code>FULL MERGE</code> Rewrite all data in overlapped files, the merge speed is slow, but there will be no redundant data on the disk eventually.</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; MERGE
IoTDB&gt; FULL MERGE
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h2 id="clear-cache"><a href="#clear-cache" class="header-anchor">#</a> CLEAR CACHE</h2> <p>Clear the cache of chunk, chunk metadata and timeseries metadata to release the memory footprint.</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; CLEAR CACHE
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h2 id="create-snapshot-for-schema"><a href="#create-snapshot-for-schema" class="header-anchor">#</a> CREATE SNAPSHOT FOR SCHEMA</h2> <p>To speed up restarting of IoTDB, users can create snapshot of schema and avoid recovering schema from mlog file.</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>IoTDB&gt; CREATE SNAPSHOT FOR SCHEMA
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div></div> <div class="page-nav"><p class="inner"><span class="prev">
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