| import{_ as s,c as a,b as n,o as t}from"./app-qnr2m1Dh.js";const l={};function i(r,e){return t(),a("div",null,e[0]||(e[0]=[n(`<h2 id="最新点查询" tabindex="-1"><a class="header-anchor" href="#最新点查询"><span>最新点查询</span></a></h2><p>最新点查询是时序数据库 Apache IoTDB 中提供的一种特殊查询，最新点查询返回时间序列中时间戳最大的数据点，即一条序列的最新状态。用户可以通过 <code>select last</code> 指定查询最新点。由于最新点数据表征了当前状态，因此在物联网数据分析场景中尤为重要。为了提供毫秒级的返回速度，Apache IoTDB 对最新点查询进行了缓存优化**，**满足用户对设备实时监控的性能需求。</p><p>SQL 语法：</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> |
| <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>其含义是：查询时间序列 prefixPath.path 中最近时间戳的数据。</p><p><code>whereClause</code> 中当前只支持含有 <code>></code> 或 <code>>=</code> 的时间过滤条件，任何其他过滤条件都将会返回异常。</p><p>结果集为四列的结构：</p><div class="language-text line-numbers-mode" data-highlighter="prismjs" data-ext="text" data-title="text"><pre><code><span class="line">+----+----------+-----+--------+</span> |
| <span class="line">|Time|timeseries|value|dataType|</span> |
| <span class="line">+----+----------+-----+--------+</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></div><p><strong>示例 1：</strong> 查询 root.ln.wf01.wt01.status 的最新数据点</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>示例 2：</strong> 查询 root.ln.wf01.wt01 下 status，temperature 时间戳大于等于 2017-11-07T23:50:00 的最新数据点。</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>`,12)]))}const o=s(l,[["render",i],["__file","Last-Query.html.vue"]]),c=JSON.parse('{"path":"/zh/UserGuide/V0.13.x/Query-Data/Last-Query.html","title":"","lang":"zh-CN","frontmatter":{"description":"最新点查询 最新点查询是时序数据库 Apache IoTDB 中提供的一种特殊查询，最新点查询返回时间序列中时间戳最大的数据点，即一条序列的最新状态。用户可以通过 select last 指定查询最新点。由于最新点数据表征了当前状态，因此在物联网数据分析场景中尤为重要。为了提供毫秒级的返回速度，Apache IoTDB 对最新点查询进行了缓存优化**，...","head":[["link",{"rel":"alternate","hreflang":"en-us","href":"https://iotdb.apache.org/UserGuide/V0.13.x/Query-Data/Last-Query.html"}],["meta",{"property":"og:url","content":"https://iotdb.apache.org/zh/UserGuide/V0.13.x/Query-Data/Last-Query.html"}],["meta",{"property":"og:site_name","content":"IoTDB Website"}],["meta",{"property":"og:description","content":"最新点查询 最新点查询是时序数据库 Apache IoTDB 中提供的一种特殊查询，最新点查询返回时间序列中时间戳最大的数据点，即一条序列的最新状态。用户可以通过 select last 指定查询最新点。由于最新点数据表征了当前状态，因此在物联网数据分析场景中尤为重要。为了提供毫秒级的返回速度，Apache IoTDB 对最新点查询进行了缓存优化**，..."}],["meta",{"property":"og:type","content":"article"}],["meta",{"property":"og:locale","content":"zh-CN"}],["meta",{"property":"og:locale:alternate","content":"en-US"}],["meta",{"property":"og:updated_time","content":"2023-07-10T03:11:17.000Z"}],["meta",{"property":"article:modified_time","content":"2023-07-10T03:11:17.000Z"}],["script",{"type":"application/ld+json"},"{\\"@context\\":\\"https://schema.org\\",\\"@type\\":\\"Article\\",\\"headline\\":\\"\\",\\"image\\":[\\"\\"],\\"dateModified\\":\\"2023-07-10T03:11:17.000Z\\",\\"author\\":[]}"]]},"headers":[{"level":2,"title":"最新点查询","slug":"最新点查询","link":"#最新点查询","children":[]}],"git":{"createdTime":1688958677000,"updatedTime":1688958677000,"contributors":[{"name":"CritasWang","email":"critas@outlook.com","commits":1}]},"readingTime":{"minutes":1.51,"words":452},"filePathRelative":"zh/UserGuide/V0.13.x/Query-Data/Last-Query.md","localizedDate":"2023年7月10日","autoDesc":true}');export{o as comp,c as data}; |
