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01-33.473-33.473V143.657H180.6A134.314 134.314 0 0046.66 277.595v535.756A134.314 134.314 0 00180.6 947.289h669.74a134.36 134.36 0 00133.94-133.938V277.595a134.314 134.314 0 00-133.94-133.938zm33.473 267.877H147.126a33.145 33.145 0 01-33.473-33.473c0-18.752 14.72-33.473 33.473-33.473h736.687c18.752 0 33.472 14.72 33.472 33.473a33.145 33.145 0 01-33.472 33.473z"></path></svg><span><!----></span><meta property="datePublished" content="2023-07-10T03:11:17.000Z"></span><!----><span class="page-reading-time-info" aria-label="Reading Time"><svg xmlns="http://www.w3.org/2000/svg" class="icon timer-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="timer icon" name="timer"><path d="M799.387 122.15c4.402-2.978 7.38-7.897 7.38-13.463v-1.165c0-8.933-7.38-16.312-16.312-16.312H256.33c-8.933 0-16.311 7.38-16.311 16.312v1.165c0 5.825 2.977 10.874 7.637 13.592 4.143 194.44 97.22 354.963 220.201 392.763-122.204 37.542-214.893 196.511-220.2 389.397-4.661 5.049-7.638 11.651-7.638 19.03v5.825h566.49v-5.825c0-7.379-2.849-13.981-7.509-18.9-5.049-193.016-97.867-351.985-220.2-389.527 123.24-37.67 216.446-198.453 220.588-392.892zM531.16 450.445v352.632c117.674 1.553 211.787 40.778 211.787 88.676H304.097c0-48.286 95.149-87.382 213.728-88.676V450.445c-93.077-3.107-167.901-81.297-167.901-177.093 0-8.803 6.99-15.793 15.793-15.793 8.803 0 15.794 6.99 15.794 15.793 0 80.261 63.69 145.635 142.01 145.635s142.011-65.374 142.011-145.635c0-8.803 6.99-15.793 15.794-15.793s15.793 6.99 15.793 15.793c0 95.019-73.789 172.82-165.96 177.093z"></path></svg><span>About 2 min</span><meta property="timeRequired" content="PT2M"></span><!----><!----></div><hr></div><!----><!----><div class="theme-hope-content"><h1 id="last-query" tabindex="-1"><a class="header-anchor" href="#last-query"><span>Last Query</span></a></h1><p>The last query is a special type of query in Apache IoTDB. It returns the data point with the largest timestamp of the specified time series. In other word, it returns the latest state of a time series. This feature is especially important in IoT data analysis scenarios. To meet the performance requirement of real-time device monitoring systems, Apache IoTDB caches the latest values of all time series to achieve microsecond read latency.</p><p>The last query is to return the most recent data point of the given timeseries in a three column format.</p><p>The SQL syntax is defined as:</p><div class="language-sql line-numbers-mode" data-highlighter="prismjs" data-ext="sql" data-title="sql"><pre><code><span class="line"><span class="token keyword">select</span> <span class="token keyword">last</span> <span class="token operator"><</span>Path<span class="token operator">></span> <span class="token punctuation">[</span>COMMA <span class="token operator"><</span>Path<span class="token operator">></span><span class="token punctuation">]</span><span class="token operator">*</span> <span class="token keyword">from</span> <span class="token operator"><</span> PrefixPath <span class="token operator">></span> <span class="token punctuation">[</span>COMMA <span class="token operator"><</span> PrefixPath <span class="token operator">></span><span class="token punctuation">]</span><span class="token operator">*</span> <span class="token operator"><</span>WhereClause<span class="token operator">></span> <span class="token punctuation">[</span><span class="token keyword">ORDER</span> <span class="token keyword">BY</span> TIMESERIES <span class="token punctuation">(</span><span class="token keyword">DESC</span> <span class="token operator">|</span> <span class="token keyword">ASC</span><span class="token punctuation">)</span>?<span class="token punctuation">]</span></span> |
| <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div></div></div><p>which means: Query and return the last data points of timeseries prefixPath.path.</p><ul><li><p>Only time filter is supported in <WhereClause>. Any other filters given in the <WhereClause> will give an exception. When the cached most recent data point does not satisfy the criterion specified by the filter, IoTDB will have to get the result from the external storage, which may cause a decrease in performance.</p></li><li><p>The result will be returned in a four column table format.</p><div class="language-text line-numbers-mode" data-highlighter="prismjs" data-ext="text" data-title="text"><pre><code><span class="line">| Time | timeseries | value | dataType |</span> |
| <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div></div></div><p><strong>Note:</strong> The <code>value</code> colum will always return the value as <code>string</code> and thus also has <code>TSDataType.TEXT</code>. Therefore, the column <code>dataType</code> is returned also which contains the <em>real</em> type how the value should be interpreted.</p></li><li><p>We can use <code>ORDER BY TIMESERIES (DESC | ASC)</code> to specify that the result set is sorted in descending/ascending order by timeseries name.</p></li></ul><p><strong>Example 1:</strong> get the last point of root.ln.wf01.wt01.status:</p><div class="language-text line-numbers-mode" data-highlighter="prismjs" data-ext="text" data-title="text"><pre><code><span class="line">IoTDB> select last status from root.ln.wf01.wt01</span> |
| <span class="line">+-----------------------------+------------------------+-----+--------+</span> |
| <span class="line">| Time| timeseries|value|dataType|</span> |
| <span class="line">+-----------------------------+------------------------+-----+--------+</span> |
| <span class="line">|2017-11-07T23:59:00.000+08:00|root.ln.wf01.wt01.status|false| BOOLEAN|</span> |
| <span class="line">+-----------------------------+------------------------+-----+--------+</span> |
| <span class="line">Total line number = 1</span> |
| <span class="line">It costs 0.000s</span> |
| <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p><strong>Example 2:</strong> get the last status and temperature points of root.ln.wf01.wt01, whose timestamp larger or equal to 2017-11-07T23:50:00。</p><div class="language-text line-numbers-mode" data-highlighter="prismjs" data-ext="text" data-title="text"><pre><code><span class="line">IoTDB> select last status, temperature from root.ln.wf01.wt01 where time >= 2017-11-07T23:50:00</span> |
| <span class="line">+-----------------------------+-----------------------------+---------+--------+</span> |
| <span class="line">| Time| timeseries| value|dataType|</span> |
| <span class="line">+-----------------------------+-----------------------------+---------+--------+</span> |
| <span class="line">|2017-11-07T23:59:00.000+08:00| root.ln.wf01.wt01.status| false| BOOLEAN|</span> |
| <span class="line">|2017-11-07T23:59:00.000+08:00|root.ln.wf01.wt01.temperature|21.067368| DOUBLE|</span> |
| <span class="line">+-----------------------------+-----------------------------+---------+--------+</span> |
| <span class="line">Total line number = 2</span> |
| <span class="line">It costs 0.002s</span> |
| <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p><strong>Example 3:</strong> get the last points of all sensor in root.ln.wf01.wt01, and order the result by the timeseries column desc</p><div class="language-text line-numbers-mode" data-highlighter="prismjs" data-ext="text" data-title="text"><pre><code><span class="line">IoTDB> select last * from root.ln.wf01.wt01 order by timeseries desc;</span> |
| <span class="line">+-----------------------------+-----------------------------+---------+--------+</span> |
| <span class="line">| Time| timeseries| value|dataType|</span> |
| <span class="line">+-----------------------------+-----------------------------+---------+--------+</span> |
| <span class="line">|2017-11-07T23:59:00.000+08:00|root.ln.wf01.wt01.temperature|21.067368| DOUBLE|</span> |
| <span class="line">|2017-11-07T23:59:00.000+08:00| root.ln.wf01.wt01.status| false| BOOLEAN|</span> |
| <span class="line">+-----------------------------+-----------------------------+---------+--------+</span> |
| <span class="line">Total line number = 2</span> |
| <span class="line">It costs 0.002s</span> |
| <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div></div><!----><footer class="vp-page-meta"><div class="vp-meta-item edit-link"><a class="auto-link external-link vp-meta-label" href="https://github.com/apache/iotdb-docs/edit/main/src/UserGuide/V1.1.x/Query-Data/Last-Query.md" aria-label="Found Error? Edit this page on GitHub" rel="noopener noreferrer" target="_blank"><!--[--><svg xmlns="http://www.w3.org/2000/svg" class="icon edit-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="edit icon" name="edit"><path d="M430.818 653.65a60.46 60.46 0 0 1-50.96-93.281l71.69-114.012 7.773-10.365L816.038 80.138A60.46 60.46 0 0 1 859.225 62a60.46 60.46 0 0 1 43.186 18.138l43.186 43.186a60.46 60.46 0 0 1 0 86.373L588.879 565.55l-8.637 8.637-117.466 68.234a60.46 60.46 0 0 1-31.958 11.229z"></path><path d="M728.802 962H252.891A190.883 190.883 0 0 1 62.008 771.98V296.934a190.883 190.883 0 0 1 190.883-192.61h267.754a60.46 60.46 0 0 1 0 120.92H252.891a69.962 69.962 0 0 0-69.098 69.099V771.98a69.962 69.962 0 0 0 69.098 69.098h475.911A69.962 69.962 0 0 0 797.9 771.98V503.363a60.46 60.46 0 1 1 120.922 0V771.98A190.883 190.883 0 0 1 728.802 962z"></path></svg><!--]-->Found Error? Edit this page on GitHub<!----></a></div><div class="vp-meta-item git-info"><div class="update-time"><span class="vp-meta-label">Last update: </span><!----></div><!----></div></footer><nav class="vp-page-nav"><a class="route-link auto-link prev" href="/UserGuide/V1.1.x/Query-Data/Select-Expression.html" aria-label="Select Expression"><div class="hint"><span class="arrow start"></span>Prev</div><div class="link"><!---->Select Expression</div></a><a class="route-link auto-link next" href="/UserGuide/V1.1.x/Query-Data/Align-By.html" aria-label="Query Alignment Mode"><div class="hint">Next<span class="arrow end"></span></div><div class="link">Query Alignment Mode<!----></div></a></nav><!----><!----><!--]--></main><!--]--><!--]--><footer style="padding-bottom:2rem;"><span id="doc-version" style="display:none;">rel/1.1</span><p style="text-align:center;color:#909399;font-size:12px;margin:0 30px;">Copyright © 2024 The Apache Software Foundation.<br> Apache IoTDB, IoTDB, Apache, the Apache feather logo, and the Apache IoTDB project logo are either registered trademarks or trademarks of The Apache Software Foundation in all countries</p><p style="text-align:center;margin-top:10px;color:#909399;font-size:12px;margin:0 30px;"><strong>Have a question?</strong> Connect with us on QQ, WeChat, or Slack. <a href="https://github.com/apache/iotdb/issues/1995">Join the community</a> now.</p></footer></div><!--]--><!--]--><!--[--><!----><!--]--><!--]--></div> |
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