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| --><h2 id="查询补空值" tabindex="-1"><a class="header-anchor" href="#查询补空值" aria-hidden="true">#</a> 查询补空值</h2><p>当对序列进行分段聚合时,某一段时间可能不存在数据,则此段数据的聚合结果为空,但这种空值不利于进行数据可视化展示和分析,需要对空值进行填补。</p><p>查询补空值允许用户按照特定的方法对查询结果填充空值,如取前一个不为空的值,或线性插值。补空值之后的查询结果能更好地反映数据分布,有利于用户进行数据分析。</p><p>在 IoTDB 中,用户可以使用 FILL 子句指定某一时间点或一时间窗口数据缺失的情况下的填充模式。如果查询点空,则填充功能将不起作用。</p><h3 id="填充方法" tabindex="-1"><a class="header-anchor" href="#填充方法" aria-hidden="true">#</a> 填充方法</h3><p>IoTDB 目前支持 <code>previous</code> , <code>linear</code>, <code>value</code> 三种空值填充方式,数据类型和支持的填充方法如下表所示:</p><table><thead><tr><th style="text-align:left;">数据类型</th><th style="text-align:left;">支持的填充方法</th></tr></thead><tbody><tr><td style="text-align:left;">boolean</td><td style="text-align:left;">previous, value</td></tr><tr><td style="text-align:left;">int32</td><td style="text-align:left;">previous, linear, value</td></tr><tr><td style="text-align:left;">int64</td><td style="text-align:left;">previous, linear, value</td></tr><tr><td style="text-align:left;">float</td><td style="text-align:left;">previous, linear, value</td></tr><tr><td style="text-align:left;">double</td><td style="text-align:left;">previous, linear, value</td></tr><tr><td style="text-align:left;">text</td><td style="text-align:left;">previous, value</td></tr></tbody></table><blockquote><p>注意:在 Fill 语句中只能指定一种填充方法。空值填充兼容 0.12 版本及以前的语法(即 fill((<data_type>[<fill_method>(, <before_range>, <after_range>)?])+)),但老的语法也不能同时指定多种填充方式。</p></blockquote><h3 id="单点补空值" tabindex="-1"><a class="header-anchor" href="#单点补空值" aria-hidden="true">#</a> 单点补空值</h3><p>当某一特定时间戳的数据为空时,可以使用单值填充对空值进行填充,详细说明如下:</p><h4 id="previous-填充" tabindex="-1"><a class="header-anchor" href="#previous-填充" aria-hidden="true">#</a> Previous 填充</h4><p>当查询的时间戳下数据为空时,将使用前一个时间戳的值来填充空白。 语法定义如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token operator"><</span>path<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 keyword">where</span> <span class="token keyword">time</span> <span class="token operator">=</span> <span class="token operator"><</span>T<span class="token operator">></span> fill<span class="token punctuation">(</span>previous<span class="token punctuation">(</span><span class="token punctuation">,</span> <span class="token operator"><</span>before_range<span class="token operator">></span><span class="token punctuation">)</span>?<span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>下表给出了所有参数的详细说明:</p><table><thead><tr><th style="text-align:left;">参数名称(不区分大小写)</th><th style="text-align:left;">解释</th></tr></thead><tbody><tr><td style="text-align:left;">path, prefixPath</td><td style="text-align:left;">查询路径; 必填项</td></tr><tr><td style="text-align:left;">T</td><td style="text-align:left;">查询时间戳(只能指定一个); 必填项</td></tr><tr><td style="text-align:left;">before_range</td><td style="text-align:left;">表示前一种方法的有效时间范围。 当 [T-before_range,T] 范围内的值存在时,前一种方法将起作用。 如果未指定 before_range,则 before_range 会使用默认值 default_fill_interval; -1 表示无穷大; 可选字段</td></tr></tbody></table><p>在这里,我们举一个使用 Previous 方法填充空值的示例。 SQL 语句如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> temperature <span class="token keyword">from</span> root<span class="token punctuation">.</span>sgcc<span class="token punctuation">.</span>wf03<span class="token punctuation">.</span>wt01 <span class="token keyword">where</span> <span class="token keyword">time</span> <span class="token operator">=</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">01</span>T16:<span class="token number">37</span>:<span class="token number">50.000</span> fill<span class="token punctuation">(</span>previous<span class="token punctuation">,</span> <span class="token number">1</span>m<span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>含义:</p><p>由于时间根目录 root.sgcc.wf03.wt01.temperature 在 2017-11-01T16:37:50.000 为空,因此系统使用以前的时间戳 2017-11-01T16:37:00.000(且时间戳位于 [2017-11-01T16:36:50.000, 2017-11-01T16:37:50.000] 范围)进行填充和显示。</p><p>在 <a href="https://github.com/thulab/iotdb/files/4438687/OtherMaterial-Sample.Data.txt" target="_blank" rel="noopener noreferrer">样例数据<span><svg class="external-link-icon" 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"><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="external-link-icon-sr-only">open in new window</span></span></a> 中, 该语句的执行结果如下所示:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+-------------------------------+ |
| | Time|root.sgcc.wf03.wt01.temperature| |
| +-----------------------------+-------------------------------+ |
| |2017-11-01T16:37:50.000+08:00| 21.93| |
| +-----------------------------+-------------------------------+ |
| Total line number = 1 |
| It costs 0.016s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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>值得注意的是,如果在指定的有效时间范围内没有值,系统将不会填充空值,如下所示:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>IoTDB> select temperature from root.sgcc.wf03.wt01 where time = 2017-11-01T16:37:50.000 fill(previous, 1s) |
| +-----------------------------+-------------------------------+ |
| | Time|root.sgcc.wf03.wt01.temperature| |
| +-----------------------------+-------------------------------+ |
| |2017-11-01T16:37:50.000+08:00| null| |
| +-----------------------------+-------------------------------+ |
| Total line number = 1 |
| It costs 0.004s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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><h4 id="linear-填充" tabindex="-1"><a class="header-anchor" href="#linear-填充" aria-hidden="true">#</a> Linear 填充</h4><p>当查询的时间戳下数据为空时,将使用前一个和下一个时间戳的值来填充空白。 语法定义如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token operator"><</span>path<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 keyword">where</span> <span class="token keyword">time</span> <span class="token operator">=</span> <span class="token operator"><</span>T<span class="token operator">></span> fill<span class="token punctuation">(</span>linear<span class="token punctuation">(</span><span class="token punctuation">,</span> <span class="token operator"><</span>before_range<span class="token operator">></span><span class="token punctuation">,</span> <span class="token operator"><</span>after_range<span class="token operator">></span><span class="token punctuation">)</span>?<span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>下表给出了所有参数的详细说明:</p><table><thead><tr><th style="text-align:left;">参数名称(不区分大小写)</th><th style="text-align:left;">解释</th></tr></thead><tbody><tr><td style="text-align:left;">path, prefixPath</td><td style="text-align:left;">查询路径; 必填项</td></tr><tr><td style="text-align:left;">T</td><td style="text-align:left;">查询时间戳(只能指定一个); 必填项</td></tr><tr><td style="text-align:left;">before_range, after_range</td><td style="text-align:left;">表示线性方法的有效时间范围。 当 [T - before_range,T + after_range] 范围内的值存在时,前一种方法将起作用。 如果未明确指定 before_range 和 after_range,则使用 default_fill_interval。 -1 表示无穷大; 可选字段</td></tr></tbody></table><p>需要注意的是一旦时间序列在查询时间戳 T 时刻存在有效值,线性填充就会使用这个值作为结果返回。 除此之外,如果在 [T - before_range, T] 或 [T, T + after_range] 两个范围中任意一个范围内不存在有效填充值,则线性填充返回 null 值。</p><p>在这里,我们举一个使用线性方法填充空值的示例。 SQL 语句如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> temperature <span class="token keyword">from</span> root<span class="token punctuation">.</span>sgcc<span class="token punctuation">.</span>wf03<span class="token punctuation">.</span>wt01 <span class="token keyword">where</span> <span class="token keyword">time</span> <span class="token operator">=</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">01</span>T16:<span class="token number">37</span>:<span class="token number">50.000</span> fill<span class="token punctuation">(</span>linear<span class="token punctuation">,</span> <span class="token number">1</span>m<span class="token punctuation">,</span> <span class="token number">1</span>m<span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>含义:</p><p>由于时间根目录 root.sgcc.wf03.wt01.temperature 在 2017-11-01T16:37:50.000 为空,因此系统使用以前的时间戳 2017-11-01T16:37:00.000(且时间戳位于 [2017-11-01T16:36:50.000,2017-11-01T16:37:50.000) 时间范围)及其值 21.927326,下一个时间戳记 2017-11-01T16:38:00.000(且时间戳记位于 (2017-11-01T16:37:50.000, 2017-11-01T16:38:50.000) 时间范围)及其值 25.311783 以执行线性拟合计算:</p><p>21.927326 +(25.311783-21.927326)/ 60s * 50s = 24.747707</p><p>在 <a href="https://github.com/thulab/iotdb/files/4438687/OtherMaterial-Sample.Data.txt" target="_blank" rel="noopener noreferrer">样例数据<span><svg class="external-link-icon" 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"><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="external-link-icon-sr-only">open in new window</span></span></a> 中, 该语句的执行结果如下所示:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+-------------------------------+ |
| | Time|root.sgcc.wf03.wt01.temperature| |
| +-----------------------------+-------------------------------+ |
| |2017-11-01T16:37:50.000+08:00| 24.747707| |
| +-----------------------------+-------------------------------+ |
| Total line number = 1 |
| It costs 0.017s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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><h4 id="value-填充" tabindex="-1"><a class="header-anchor" href="#value-填充" aria-hidden="true">#</a> Value 填充</h4><p>当查询的时间戳下数据为空时,将使用给定的值来填充空白。语法定义如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token operator"><</span>path<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 keyword">where</span> <span class="token keyword">time</span> <span class="token operator">=</span> <span class="token operator"><</span>T<span class="token operator">></span> fill<span class="token punctuation">(</span>constant<span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>下表给出了所有参数的详细说明:</p><table><thead><tr><th style="text-align:left;">参数名称(不区分大小写)</th><th style="text-align:left;">解释</th></tr></thead><tbody><tr><td style="text-align:left;">path, prefixPath</td><td style="text-align:left;">查询路径; 必填项</td></tr><tr><td style="text-align:left;">T</td><td style="text-align:left;">查询时间戳(只能指定一个); 必填项</td></tr><tr><td style="text-align:left;">constant</td><td style="text-align:left;">给定的填充值;必填项</td></tr></tbody></table><p>需要注意的是一旦时间序列在查询时间戳T时刻存在有效值,特定值填充就会使用这个值作为结果返回。</p><p>在这里,我们举一个使用特定值方法填充空值的示例。 SQL语句如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> temperature <span class="token keyword">from</span> root<span class="token punctuation">.</span>sgcc<span class="token punctuation">.</span>wf03<span class="token punctuation">.</span>wt01 <span class="token keyword">where</span> <span class="token keyword">time</span> <span class="token operator">=</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">01</span>T16:<span class="token number">37</span>:<span class="token number">50.000</span> fill<span class="token punctuation">(</span><span class="token number">2.0</span><span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>含义:</p><p>由于时间序列 root.sgcc.wf03.wt01.temperature 在 2017-11-01T16:37:50.000 为空,因此使用给定的值 2.0 进行填充:</p><p>在 <a href="https://github.com/thulab/iotdb/files/4438687/OtherMaterial-Sample.Data.txt" target="_blank" rel="noopener noreferrer">样例数据<span><svg class="external-link-icon" 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"><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="external-link-icon-sr-only">open in new window</span></span></a> 中, 该语句的执行结果如下所示:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+-------------------------------+ |
| | Time|root.sgcc.wf03.wt01.temperature| |
| +-----------------------------+-------------------------------+ |
| |2017-11-01T16:37:50.000+08:00| 2.0 | |
| +-----------------------------+-------------------------------+ |
| Total line number = 1 |
| It costs 0.007s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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>在使用 VALUE 方法填充时需要注意,如果查询结果的数据类型与输入常量值不同,IoTDB 将不进行填充</p><p>示例:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> temperature <span class="token keyword">from</span> root<span class="token punctuation">.</span>sgcc<span class="token punctuation">.</span>wf03<span class="token punctuation">.</span>wt01 <span class="token keyword">where</span> <span class="token keyword">time</span> <span class="token operator">=</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">01</span>T16:<span class="token number">37</span>:<span class="token number">50.000</span> fill<span class="token punctuation">(</span><span class="token string">'test'</span><span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>结果:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+-------------------------------+ |
| | Time|root.sgcc.wf03.wt01.temperature| |
| +-----------------------------+-------------------------------+ |
| |2017-11-01T16:37:50.000+08:00| null | |
| +-----------------------------+-------------------------------+ |
| Total line number = 1 |
| It costs 0.007s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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><h3 id="降采样补空值" tabindex="-1"><a class="header-anchor" href="#降采样补空值" aria-hidden="true">#</a> 降采样补空值</h3><p>IoTDB 支持对原降采样结果进行空值填充,<code>previous</code>、<code>linear</code>、<code>value</code> 填充方式均可作用于查询语句中的任一聚合算子,但一条查询语句只能使用一种空值填充方式。此外,使用时需要注意以下两点:</p><ul><li>在任何情形下都不会填充 <code>count</code> 的聚合结果,因为对于不存在任数据的查询区间,<code>count</code> 的结果为 0。</li><li>分类处理 sum 的聚合结果:若某个查询区间不存在任何数据,sum 的聚合结果为 null,将被 GroupByFill 填充;若某个查询区间内 sum 的聚合结果恰好为 0,那么 GroupByFill 不会填充这个值。</li></ul><p>降采样补空值查询语法同单点补空值查询语法相似,下面列出简单的示例和使用细节:</p><h4 id="previous-和-previousuntillast-的区别" tabindex="-1"><a class="header-anchor" href="#previous-和-previousuntillast-的区别" aria-hidden="true">#</a> PREVIOUS 和 PREVIOUSUNTILLAST 的区别</h4><ul><li>PREVIOUS:只要空值前边有值,就会用其填充空值。</li><li>PREVIOUSUNTILLAST:不会填充此序列最新点后的空值。</li></ul><p>首先检查一下 root.ln.wf01.wt01.temperature 在时间 2017-11-07T23:49:00 以后的值:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>IoTDB> SELECT temperature FROM root.ln.wf01.wt01 where time >= 2017-11-07T23:49:00 |
| +-----------------------------+-----------------------------+ |
| | Time|root.ln.wf01.wt01.temperature| |
| +-----------------------------+-----------------------------+ |
| |2017-11-07T23:49:00.000+08:00| 23.7| |
| |2017-11-07T23:51:00.000+08:00| 22.24| |
| |2017-11-07T23:53:00.000+08:00| 24.58| |
| |2017-11-07T23:54:00.000+08:00| 22.52| |
| |2017-11-07T23:57:00.000+08:00| 24.39| |
| |2017-11-08T00:00:00.000+08:00| 21.07| |
| +-----------------------------+-----------------------------+ |
| Total line number = 6 |
| It costs 0.010s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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 class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>root.ln.wf01.wt01.temperature 最早时间和值是 2017-11-07T23:49:00 和 23.7;最后时间和值是 2017-11-08T00:00:00 和 21.07</p><p>SQL 示例:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">SELECT</span> last_value<span class="token punctuation">(</span>temperature<span class="token punctuation">)</span> <span class="token keyword">FROM</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>wf01<span class="token punctuation">.</span>wt01 <span class="token keyword">GROUP</span> <span class="token keyword">BY</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">50</span>:<span class="token number">00</span><span class="token punctuation">,</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">59</span>:<span class="token number">00</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token number">1</span>m<span class="token punctuation">)</span> FILL <span class="token punctuation">(</span>PREVIOUSUNTILLAST<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token keyword">SELECT</span> last_value<span class="token punctuation">(</span>temperature<span class="token punctuation">)</span> <span class="token keyword">FROM</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>wf01<span class="token punctuation">.</span>wt01 <span class="token keyword">GROUP</span> <span class="token keyword">BY</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">50</span>:<span class="token number">00</span><span class="token punctuation">,</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">59</span>:<span class="token number">00</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token number">1</span>m<span class="token punctuation">)</span> FILL <span class="token punctuation">(</span>PREVIOUS<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div></div></div><p>结果:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>IoTDB> SELECT last_value(temperature) FROM root.ln.wf01.wt01 GROUP BY([2017-11-07T23:50:00, 2017-11-07T23:59:00),1m) FILL (PREVIOUSUNTILLAST); |
| +-----------------------------+-----------------------------------------+ |
| | Time|last_value(root.ln.wf01.wt01.temperature)| |
| +-----------------------------+-----------------------------------------+ |
| |2017-11-07T23:50:00.000+08:00| null| |
| |2017-11-07T23:51:00.000+08:00| 22.24| |
| |2017-11-07T23:52:00.000+08:00| 22.24| |
| |2017-11-07T23:53:00.000+08:00| 24.58| |
| |2017-11-07T23:54:00.000+08:00| 22.52| |
| |2017-11-07T23:55:00.000+08:00| 22.52| |
| |2017-11-07T23:56:00.000+08:00| 22.52| |
| |2017-11-07T23:57:00.000+08:00| 24.39| |
| |2017-11-07T23:58:00.000+08:00| null| |
| +-----------------------------+-----------------------------------------+ |
| Total line number = 9 |
| It costs 0.007s |
| |
| IoTDB> SELECT last_value(temperature) FROM root.ln.wf01.wt01 GROUP BY([2017-11-07T23:50:00, 2017-11-07T23:59:00),1m) FILL (PREVIOUS); |
| +-----------------------------+-----------------------------------------+ |
| | Time|last_value(root.ln.wf01.wt01.temperature)| |
| +-----------------------------+-----------------------------------------+ |
| |2017-11-07T23:50:00.000+08:00| null| |
| |2017-11-07T23:51:00.000+08:00| 22.24| |
| |2017-11-07T23:52:00.000+08:00| 22.24| |
| |2017-11-07T23:53:00.000+08:00| 24.58| |
| |2017-11-07T23:54:00.000+08:00| 22.52| |
| |2017-11-07T23:55:00.000+08:00| 22.52| |
| |2017-11-07T23:56:00.000+08:00| 22.52| |
| |2017-11-07T23:57:00.000+08:00| 24.39| |
| |2017-11-07T23:58:00.000+08:00| 24.39| |
| +-----------------------------+-----------------------------------------+ |
| Total line number = 9 |
| It costs 0.006s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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 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 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 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>解释:</p><p>使用 PREVIOUSUNTILLAST 将不会填充 2017-11-07T23:57:00 以后的值。</p><h4 id="第一个值与最后一个值的填充" tabindex="-1"><a class="header-anchor" href="#第一个值与最后一个值的填充" aria-hidden="true">#</a> 第一个值与最后一个值的填充</h4><p>IoTDB 的空值填充方式可以分为 PreviousFill, LinearFill, ValueFill 三大类。其中,PreviousFill 需要知道空值前的第一个非空数据,LinearFill 需要知道空值前后的第一个非空数据才能进行填充。假使某条查询语句返回的结果中第一个或最后一个值为空,就可能导致结果集在首尾存在一段连续的空值,不满足 GroupByFill 的业务期望。</p><p>在上例中,第一个时间区间 [2017-11-07T23:50:00, 2017-11-07T23:51:00) 内没有任何数据,上一个有数据的时间区间是 [2017-11-01T23:49:00, 2017-11-07T23:50:00),可以通过设置 PREVIOUS 填充向前查询参数 beforeRange 来填充第一个区间的数据,示例如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">SELECT</span> last_value<span class="token punctuation">(</span>temperature<span class="token punctuation">)</span> <span class="token keyword">FROM</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>wf01<span class="token punctuation">.</span>wt01 <span class="token keyword">GROUP</span> <span class="token keyword">BY</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">50</span>:<span class="token number">00</span><span class="token punctuation">,</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">59</span>:<span class="token number">00</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token number">1</span>m<span class="token punctuation">)</span> FILL <span class="token punctuation">(</span>PREVIOUS<span class="token punctuation">,</span> <span class="token number">1</span>m<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>结果:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>IoTDB> SELECT last_value(temperature) FROM root.ln.wf01.wt01 GROUP BY([2017-11-07T23:50:00, 2017-11-07T23:59:00),1m) FILL (PREVIOUS, 1m); |
| +-----------------------------+-----------------------------------------+ |
| | Time|last_value(root.ln.wf01.wt01.temperature)| |
| +-----------------------------+-----------------------------------------+ |
| |2017-11-07T23:50:00.000+08:00| 23.7| |
| |2017-11-07T23:51:00.000+08:00| 22.24| |
| |2017-11-07T23:52:00.000+08:00| 22.24| |
| |2017-11-07T23:53:00.000+08:00| 24.58| |
| |2017-11-07T23:54:00.000+08:00| 22.52| |
| |2017-11-07T23:55:00.000+08:00| 22.52| |
| |2017-11-07T23:56:00.000+08:00| null| |
| |2017-11-07T23:57:00.000+08:00| 24.39| |
| |2017-11-07T23:58:00.000+08:00| 24.39| |
| +-----------------------------+-----------------------------------------+ |
| Total line number = 9 |
| It costs 0.005s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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 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>解释:</p><p>为了不与原有语义冲突,当不设置 before_range, after_range 参数时,GroupByFill 的空值填充取空值的前一个/后一个非空值完成;当设置 before_range, after_range 参数时,设空值所在记录的时间戳为 t,GroupByFill 取 [t-before_range, t+after_range) 内的前一个/后一个非空值完成填充。</p><p>因为时间区间 [2017-11-07T23:55:00, 2017-11-07T23:57:00) 内均没有数据,所以本例虽然通过设置 before_range 填充了 [2017-11-07T23:50:00, 2017-11-07T23:51:00) 的数据,但由于 before_range 较小,[2017-11-07T23:56:00, 2017-11-07T23:57:00) 的数据无法填充。</p><p>before_range, after_range 参数也可辅助 LINEAR 方式进行填充,示例如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">SELECT</span> last_value<span class="token punctuation">(</span>temperature<span class="token punctuation">)</span> <span class="token keyword">FROM</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>wf01<span class="token punctuation">.</span>wt01 <span class="token keyword">GROUP</span> <span class="token keyword">BY</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">50</span>:<span class="token number">00</span><span class="token punctuation">,</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">59</span>:<span class="token number">00</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token number">1</span>m<span class="token punctuation">)</span> FILL <span class="token punctuation">(</span>LINEAR<span class="token punctuation">,</span> <span class="token number">5</span>m<span class="token punctuation">,</span> <span class="token number">5</span>m<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>结果:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>IoTDB> SELECT last_value(temperature) FROM root.ln.wf01.wt01 GROUP BY([2017-11-07T23:50:00, 2017-11-07T23:59:00),1m) FILL (LINEAR, 5m, 5m); |
| +-----------------------------+-----------------------------------------+ |
| | Time|last_value(root.ln.wf01.wt01.temperature)| |
| +-----------------------------+-----------------------------------------+ |
| |2017-11-07T23:50:00.000+08:00| 22.970001| |
| |2017-11-07T23:51:00.000+08:00| 22.24| |
| |2017-11-07T23:52:00.000+08:00| 23.41| |
| |2017-11-07T23:53:00.000+08:00| 24.58| |
| |2017-11-07T23:54:00.000+08:00| 22.52| |
| |2017-11-07T23:55:00.000+08:00| 23.143333| |
| |2017-11-07T23:56:00.000+08:00| 23.766666| |
| |2017-11-07T23:57:00.000+08:00| 24.39| |
| |2017-11-07T23:58:00.000+08:00| 23.283333| |
| +-----------------------------+-----------------------------------------+ |
| Total line number = 9 |
| It costs 0.008s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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 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><blockquote><p>注意:设原始降采样查询区间为 [start_time, end_time),在指定 before_range, after_range 参数后,降采样查询结果不变,但查询区间将转变为 [start_time - before_range, end_time + after_range)。因此这两个参数设置较大时会影响效率,使用时需注意。</p></blockquote><h4 id="value-填充-1" tabindex="-1"><a class="header-anchor" href="#value-填充-1" aria-hidden="true">#</a> Value 填充</h4><p>值填充方式会将输入的常量值解析为字符串,填充时尝试将字符串常量转换为对应类型的数据,若转换成功则进行填充,否则就不填充。举例如下:</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">SELECT</span> last_value<span class="token punctuation">(</span>temperature<span class="token punctuation">)</span> <span class="token keyword">FROM</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>wf01<span class="token punctuation">.</span>wt01 <span class="token keyword">GROUP</span> <span class="token keyword">BY</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">50</span>:<span class="token number">00</span><span class="token punctuation">,</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">59</span>:<span class="token number">00</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token number">1</span>m<span class="token punctuation">)</span> FILL <span class="token punctuation">(</span><span class="token number">20.0</span><span class="token punctuation">)</span> |
| <span class="token keyword">SELECT</span> last_value<span class="token punctuation">(</span>temperature<span class="token punctuation">)</span> <span class="token keyword">FROM</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>wf01<span class="token punctuation">.</span>wt01 <span class="token keyword">GROUP</span> <span class="token keyword">BY</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">50</span>:<span class="token number">00</span><span class="token punctuation">,</span> <span class="token number">2017</span><span class="token operator">-</span><span class="token number">11</span><span class="token operator">-</span><span class="token number">07</span>T23:<span class="token number">59</span>:<span class="token number">00</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token number">1</span>m<span class="token punctuation">)</span> FILL <span class="token punctuation">(</span><span class="token string">'temperature'</span><span class="token punctuation">)</span> |
| </code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div></div></div><p>结果:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>IoTDB> SELECT last_value(temperature) FROM root.ln.wf01.wt01 GROUP BY([2017-11-07T23:50:00, 2017-11-07T23:59:00),1m) FILL (20.0); |
| +-----------------------------+-----------------------------------------+ |
| | Time|last_value(root.ln.wf01.wt01.temperature)| |
| +-----------------------------+-----------------------------------------+ |
| |2017-11-07T23:50:00.000+08:00| 20.0| |
| |2017-11-07T23:51:00.000+08:00| 22.24| |
| |2017-11-07T23:52:00.000+08:00| 20.0| |
| |2017-11-07T23:53:00.000+08:00| 24.58| |
| |2017-11-07T23:54:00.000+08:00| 22.52| |
| |2017-11-07T23:55:00.000+08:00| 20.0| |
| |2017-11-07T23:56:00.000+08:00| 20.0| |
| |2017-11-07T23:57:00.000+08:00| 24.39| |
| |2017-11-07T23:58:00.000+08:00| 20.0| |
| +-----------------------------+-----------------------------------------+ |
| Total line number = 9 |
| It costs 0.007s |
| |
| IoTDB> SELECT last_value(temperature) FROM root.ln.wf01.wt01 GROUP BY([2017-11-07T23:50:00, 2017-11-07T23:59:00),1m) FILL ('temperature'); |
| +-----------------------------+-----------------------------------------+ |
| | Time|last_value(root.ln.wf01.wt01.temperature)| |
| +-----------------------------+-----------------------------------------+ |
| |2017-11-07T23:50:00.000+08:00| null| |
| |2017-11-07T23:51:00.000+08:00| 22.24| |
| |2017-11-07T23:52:00.000+08:00| null| |
| |2017-11-07T23:53:00.000+08:00| 24.58| |
| |2017-11-07T23:54:00.000+08:00| 22.52| |
| |2017-11-07T23:55:00.000+08:00| null| |
| |2017-11-07T23:56:00.000+08:00| null| |
| |2017-11-07T23:57:00.000+08:00| 24.39| |
| |2017-11-07T23:58:00.000+08:00| null| |
| +-----------------------------+-----------------------------------------+ |
| Total line number = 9 |
| It costs 0.005s |
| </code></pre><div class="line-numbers" aria-hidden="true"><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 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 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 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="page-meta"><div class="meta-item edit-link"><a href="https://github.com/apache/iotdb/edit/rel/0.13/docs/zh/UserGuide/Query-Data/Fill-Null-Value.md" rel="noopener noreferrer" target="_blank" aria-label="发现错误?在 GitHub 上编辑此页" class="nav-link label"><!--[--><svg xmlns="http://www.w3.org/2000/svg" class="icon edit-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="edit icon"><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><!--]-->发现错误?在 GitHub 上编辑此页<span><svg class="external-link-icon" 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"><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="external-link-icon-sr-only">open in new window</span></span><!----></a></div><div class="meta-item git-info"><!----><!----></div></footer><nav class="page-nav"><a href="/zh/UserGuide/V0.13.x/Query-Data/Last-Query.html" class="nav-link prev" aria-label="最新点查询"><div class="hint"><span class="arrow start"></span>上一页</div><div class="link"><!---->最新点查询</div></a><a href="/zh/UserGuide/V0.13.x/Query-Data/Without-Null.html" class="nav-link next" aria-label="空值过滤"><div class="hint">下一页<span class="arrow end"></span></div><div class="link">空值过滤<!----></div></a></nav><!----><!----><!--]--></main><!--]--><footer style="padding-bottom:2rem;"><span id="doc-version" style="display:none;">rel/0.13</span><p style="text-align:center;color:#909399;font-size:12px;margin:0 30px;">Copyright © 2023 The Apache Software Foundation.<br> Apache and the Apache feather logo are trademarks of The Apache Software Foundation</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><p style="text-align:center;margin-top:10px;color:#909399;font-size:12px;margin:0 30px;"> We use <a href="https://analytics.google.com">Google Analytics</a> to collect anonymous, aggregated usage information. </p></footer></div><!--]--><!--]--><!----><!--]--></div> |
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