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--><h2 id="条件表达式" tabindex="-1"><a class="header-anchor" href="#条件表达式" aria-hidden="true">#</a> 条件表达式</h2><h3 id="case" tabindex="-1"><a class="header-anchor" href="#case" aria-hidden="true">#</a> CASE</h3><h4 id="介绍" tabindex="-1"><a class="header-anchor" href="#介绍" aria-hidden="true">#</a> 介绍</h4><p>CASE表达式是一种条件表达式，可用于根据特定条件返回不同的值，功能类似于其它语言中的if-else。 CASE表达式由以下部分组成：</p><ul><li>CASE关键字：表示开始CASE表达式。</li><li>WHEN-THEN子句：可能存在多个，用于定义条件与给出结果。此子句又分为WHEN和THEN两个部分，WHEN部分表示条件，THEN部分表示结果表达式。如果WHEN条件为真，则返回对应的THEN结果。</li><li>ELSE子句：如果没有任何WHEN-THEN子句的条件为真，则返回ELSE子句中的结果。可以不存在ELSE子句。</li><li>END关键字：表示结束CASE表达式。</li></ul><p>CASE表达式是一种标量运算，可以配合任何其它的标量运算或聚合函数使用。</p><p>下文把所有THEN部分和ELSE子句并称为结果子句。</p><h4 id="语法示例" tabindex="-1"><a class="header-anchor" href="#语法示例" aria-hidden="true">#</a> 语法示例</h4><p>CASE表达式支持两种格式。</p><p>语法示例如下：</p><ul><li>格式1：</li></ul><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code> <span class="token keyword">CASE</span>
<span class="token keyword">WHEN</span> condition1 <span class="token keyword">THEN</span> expression1
<span class="token punctuation">[</span><span class="token keyword">WHEN</span> condition2 <span class="token keyword">THEN</span> expression2<span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">[</span><span class="token keyword">ELSE</span> expression_end<span class="token punctuation">]</span>
<span class="token keyword">END</span>
</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></div><p>从上至下检查WHEN子句中的condition。</p><p>condition为真时返回对应THEN子句中的expression，condition为假时继续检查下一个WHEN子句中的condition。</p><ul><li>格式2：</li></ul><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code> <span class="token keyword">CASE</span> caseValue
<span class="token keyword">WHEN</span> whenValue1 <span class="token keyword">THEN</span> expression1
<span class="token punctuation">[</span><span class="token keyword">WHEN</span> whenValue2 <span class="token keyword">THEN</span> expression2<span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">[</span><span class="token keyword">ELSE</span> expression_end<span class="token punctuation">]</span>
<span class="token keyword">END</span>
</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></div><p>从上至下检查WHEN子句中的whenValue是否与caseValue相等。</p><p>满足caseValue=whenValue时返回对应THEN子句中的expression，不满足时继续检查下一个WHEN子句中的whenValue。</p><p>格式2会被iotdb转换成等效的格式1，例如以上sql语句会转换成：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code> <span class="token keyword">CASE</span>
<span class="token keyword">WHEN</span> caseValue<span class="token operator">=</span>whenValue1 <span class="token keyword">THEN</span> expression1
<span class="token punctuation">[</span><span class="token keyword">WHEN</span> caseValue<span class="token operator">=</span>whenValue1 <span class="token keyword">THEN</span> expression1<span class="token punctuation">]</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">[</span><span class="token keyword">ELSE</span> expression_end<span class="token punctuation">]</span>
<span class="token keyword">END</span>
</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></div><p>如果格式1中的condition均不为真，或格式2中均不满足caseVaule=whenValue，则返回ELSE子句中的expression_end；不存在ELSE子句则返回null。</p><h4 id="注意事项" tabindex="-1"><a class="header-anchor" href="#注意事项" aria-hidden="true">#</a> 注意事项</h4><ul><li>格式1中，所有WHEN子句必须返回BOOLEAN类型。</li><li>格式2中，所有WHEN子句必须能够与CASE子句进行判等。</li><li>一个CASE表达式中所有结果子句的返回值类型需要满足一定的条件： <ul><li>BOOLEAN类型不能与其它类型共存，存在其它类型会报错。</li><li>TEXT类型不能与其它类型共存，存在其它类型会报错。</li><li>其它四种数值类型可以共存，最终结果会为DOUBLE类型，转换过程可能会存在精度损失。</li></ul></li><li>CASE表达式没有实现惰性计算，即所有子句都会被计算。</li><li>CASE表达式不支持与UDF混用。</li><li>CASE表达式内部不能存在聚合函数，但CASE表达式的结果可以提供给聚合函数。</li><li>使用CLI时，由于CASE表达式字符串较长，推荐用as为表达式提供别名。</li></ul><h4 id="使用示例" tabindex="-1"><a class="header-anchor" href="#使用示例" aria-hidden="true">#</a> 使用示例</h4><h5 id="示例1" tabindex="-1"><a class="header-anchor" href="#示例1" aria-hidden="true">#</a> 示例1</h5><p>CASE表达式可对数据进行直观地分析，例如：</p><ul><li>某种化学产品的制备需要温度和压力都处于特定范围之内</li><li>在制备过程中传感器会侦测温度和压力，在iotdb中形成T(temperature)和P(pressure)两个时间序列</li></ul><p>这种应用场景下，CASE表达式可以指出哪些时间的参数是合适的，哪些时间的参数不合适，以及为什么不合适。</p><p>数据：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code>IoTDB<span class="token operator">&gt;</span> <span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test1
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+------------+</span>
<span class="token operator">|</span> <span class="token keyword">Time</span><span class="token operator">|</span>root<span class="token punctuation">.</span>test1<span class="token punctuation">.</span>P<span class="token operator">|</span>root<span class="token punctuation">.</span>test1<span class="token punctuation">.</span>T<span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+------------+</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">29</span>T11:<span class="token number">25</span>:<span class="token number">54.724</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">1000000.0</span><span class="token operator">|</span> <span class="token number">1025.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">29</span>T11:<span class="token number">26</span>:<span class="token number">13.445</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">1000094.0</span><span class="token operator">|</span> <span class="token number">1040.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">29</span>T11:<span class="token number">27</span>:<span class="token number">36.988</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">1000095.0</span><span class="token operator">|</span> <span class="token number">1041.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">29</span>T11:<span class="token number">27</span>:<span class="token number">56.446</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">1000095.0</span><span class="token operator">|</span> <span class="token number">1059.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">29</span>T11:<span class="token number">28</span>:<span class="token number">20.838</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">1200000.0</span><span class="token operator">|</span> <span class="token number">1040.0</span><span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+------------+</span>
</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></div><p>SQL语句：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> T<span class="token punctuation">,</span> P<span class="token punctuation">,</span> <span class="token keyword">case</span>
<span class="token keyword">when</span> <span class="token number">1000</span><span class="token operator">&lt;</span>T <span class="token operator">and</span> T<span class="token operator">&lt;</span><span class="token number">1050</span> <span class="token operator">and</span> <span class="token number">1000000</span><span class="token operator">&lt;</span>P <span class="token operator">and</span> P<span class="token operator">&lt;</span><span class="token number">1100000</span> <span class="token keyword">then</span> <span class="token string">&quot;good!&quot;</span>
<span class="token keyword">when</span> T<span class="token operator">&lt;=</span><span class="token number">1000</span> <span class="token operator">or</span> T<span class="token operator">&gt;=</span><span class="token number">1050</span> <span class="token keyword">then</span> <span class="token string">&quot;bad temperature&quot;</span>
<span class="token keyword">when</span> P<span class="token operator">&lt;=</span><span class="token number">1000000</span> <span class="token operator">or</span> P<span class="token operator">&gt;=</span><span class="token number">1100000</span> <span class="token keyword">then</span> <span class="token string">&quot;bad pressure&quot;</span>
<span class="token keyword">end</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>result<span class="token punctuation">`</span></span>
<span class="token keyword">from</span> root<span class="token punctuation">.</span>test1
</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></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+------------+------------+---------------+
| Time|root.test1.T|root.test1.P| result|
+-----------------------------+------------+------------+---------------+
|2023-03-29T11:25:54.724+08:00| 1025.0| 1000000.0| bad pressure|
|2023-03-29T11:26:13.445+08:00| 1040.0| 1000094.0| good!|
|2023-03-29T11:27:36.988+08:00| 1041.0| 1000095.0| good!|
|2023-03-29T11:27:56.446+08:00| 1059.0| 1000095.0|bad temperature|
|2023-03-29T11:28:20.838+08:00| 1040.0| 1200000.0| bad pressure|
+-----------------------------+------------+------------+---------------+
</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></div><h5 id="示例2" tabindex="-1"><a class="header-anchor" href="#示例2" aria-hidden="true">#</a> 示例2</h5><p>CASE表达式可实现结果的自由转换，例如将具有某种模式的字符串转换成另一种字符串。</p><p>数据：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code>IoTDB<span class="token operator">&gt;</span> <span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test2
<span class="token operator">+</span><span class="token comment">-----------------------------+--------------+</span>
<span class="token operator">|</span> <span class="token keyword">Time</span><span class="token operator">|</span>root<span class="token punctuation">.</span>test2<span class="token punctuation">.</span>str<span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+--------------+</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">23</span>:<span class="token number">33.427</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> abccd<span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">23</span>:<span class="token number">39.389</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> abcdd<span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">23</span>:<span class="token number">43.463</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> abcdefg<span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+--------------+</span>
</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><p>SQL语句：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> str<span class="token punctuation">,</span> <span class="token keyword">case</span>
<span class="token keyword">when</span> str <span class="token operator">like</span> <span class="token string">&quot;%cc%&quot;</span> <span class="token keyword">then</span> <span class="token string">&quot;has cc&quot;</span>
<span class="token keyword">when</span> str <span class="token operator">like</span> <span class="token string">&quot;%dd%&quot;</span> <span class="token keyword">then</span> <span class="token string">&quot;has dd&quot;</span>
<span class="token keyword">else</span> <span class="token string">&quot;no cc and dd&quot;</span> <span class="token keyword">end</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>result<span class="token punctuation">`</span></span>
<span class="token keyword">from</span> root<span class="token punctuation">.</span>test2
</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></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+--------------+------------+
| Time|root.test2.str| result|
+-----------------------------+--------------+------------+
|2023-03-27T18:23:33.427+08:00| abccd| has cc|
|2023-03-27T18:23:39.389+08:00| abcdd| has dd|
|2023-03-27T18:23:43.463+08:00| abcdefg|no cc and dd|
+-----------------------------+--------------+------------+
</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><h5 id="示例3-搭配聚合函数" tabindex="-1"><a class="header-anchor" href="#示例3-搭配聚合函数" aria-hidden="true">#</a> 示例3：搭配聚合函数</h5><h6 id="合法-聚合函数←case表达式" tabindex="-1"><a class="header-anchor" href="#合法-聚合函数←case表达式" aria-hidden="true">#</a> 合法：聚合函数←CASE表达式</h6><p>CASE表达式可作为聚合函数的参数。例如，与聚合函数COUNT搭配，可实现同时按多个条件进行数据统计。</p><p>数据：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code>IoTDB<span class="token operator">&gt;</span> <span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test3
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+</span>
<span class="token operator">|</span> <span class="token keyword">Time</span><span class="token operator">|</span>root<span class="token punctuation">.</span>test3<span class="token punctuation">.</span>x<span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">11.300</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">0.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">14.658</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">1.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">15.981</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">2.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">17.668</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">3.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">19.112</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">4.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">20.822</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">5.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">22.462</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">6.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">24.174</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">7.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">25.858</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">8.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">2023</span><span class="token operator">-</span><span class="token number">03</span><span class="token operator">-</span><span class="token number">27</span>T18:<span class="token number">11</span>:<span class="token number">27.979</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">9.0</span><span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+</span>
</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></div><p>SQL语句：</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 function">count</span><span class="token punctuation">(</span><span class="token keyword">case</span> <span class="token keyword">when</span> x<span class="token operator">&lt;=</span><span class="token number">1</span> <span class="token keyword">then</span> <span class="token number">1</span> <span class="token keyword">end</span><span class="token punctuation">)</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>(-∞,1]<span class="token punctuation">`</span></span><span class="token punctuation">,</span>
<span class="token function">count</span><span class="token punctuation">(</span><span class="token keyword">case</span> <span class="token keyword">when</span> <span class="token number">1</span><span class="token operator">&lt;</span>x <span class="token operator">and</span> x<span class="token operator">&lt;=</span><span class="token number">3</span> <span class="token keyword">then</span> <span class="token number">1</span> <span class="token keyword">end</span><span class="token punctuation">)</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>(1,3]<span class="token punctuation">`</span></span><span class="token punctuation">,</span>
<span class="token function">count</span><span class="token punctuation">(</span><span class="token keyword">case</span> <span class="token keyword">when</span> <span class="token number">3</span><span class="token operator">&lt;</span>x <span class="token operator">and</span> x<span class="token operator">&lt;=</span><span class="token number">7</span> <span class="token keyword">then</span> <span class="token number">1</span> <span class="token keyword">end</span><span class="token punctuation">)</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>(3,7]<span class="token punctuation">`</span></span><span class="token punctuation">,</span>
<span class="token function">count</span><span class="token punctuation">(</span><span class="token keyword">case</span> <span class="token keyword">when</span> <span class="token number">7</span><span class="token operator">&lt;</span>x <span class="token keyword">then</span> <span class="token number">1</span> <span class="token keyword">end</span><span class="token punctuation">)</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>(7,+∞)<span class="token punctuation">`</span></span>
<span class="token keyword">from</span> root<span class="token punctuation">.</span>test3
</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></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+------+-----+-----+------+
|(-∞,1]|(1,3]|(3,7]|(7,+∞)|
+------+-----+-----+------+
| 2| 2| 4| 2|
+------+-----+-----+------+
</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></div><h6 id="非法-case表达式←聚合函数" tabindex="-1"><a class="header-anchor" href="#非法-case表达式←聚合函数" aria-hidden="true">#</a> 非法：CASE表达式←聚合函数</h6><p>不支持在CASE表达式内部使用聚合函数。</p><p>SQL语句：</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 keyword">case</span> <span class="token keyword">when</span> x<span class="token operator">&lt;=</span><span class="token number">1</span> <span class="token keyword">then</span> <span class="token function">avg</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span> <span class="token keyword">else</span> <span class="token function">sum</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span> <span class="token keyword">end</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test3
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>Msg: 701: Raw data and aggregation result hybrid calculation is not supported.
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><h5 id="示例4-格式2" tabindex="-1"><a class="header-anchor" href="#示例4-格式2" aria-hidden="true">#</a> 示例4：格式2</h5><p>一个使用格式2的简单例子。如果所有条件都为判等，则推荐使用格式2，以简化SQL语句。</p><p>数据：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code>IoTDB<span class="token operator">&gt;</span> <span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test4
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+</span>
<span class="token operator">|</span> <span class="token keyword">Time</span><span class="token operator">|</span>root<span class="token punctuation">.</span>test4<span class="token punctuation">.</span>x<span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+</span>
<span class="token operator">|</span><span class="token number">1970</span><span class="token operator">-</span><span class="token number">01</span><span class="token operator">-</span><span class="token number">01</span>T08:<span class="token number">00</span>:<span class="token number">00.001</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">1.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">1970</span><span class="token operator">-</span><span class="token number">01</span><span class="token operator">-</span><span class="token number">01</span>T08:<span class="token number">00</span>:<span class="token number">00.002</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">2.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">1970</span><span class="token operator">-</span><span class="token number">01</span><span class="token operator">-</span><span class="token number">01</span>T08:<span class="token number">00</span>:<span class="token number">00.003</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">3.0</span><span class="token operator">|</span>
<span class="token operator">|</span><span class="token number">1970</span><span class="token operator">-</span><span class="token number">01</span><span class="token operator">-</span><span class="token number">01</span>T08:<span class="token number">00</span>:<span class="token number">00.004</span><span class="token operator">+</span><span class="token number">08</span>:<span class="token number">00</span><span class="token operator">|</span> <span class="token number">4.0</span><span class="token operator">|</span>
<span class="token operator">+</span><span class="token comment">-----------------------------+------------+</span>
</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></div><p>SQL语句：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> x<span class="token punctuation">,</span> <span class="token keyword">case</span> x <span class="token keyword">when</span> <span class="token number">1</span> <span class="token keyword">then</span> <span class="token string">&quot;one&quot;</span> <span class="token keyword">when</span> <span class="token number">2</span> <span class="token keyword">then</span> <span class="token string">&quot;two&quot;</span> <span class="token keyword">else</span> <span class="token string">&quot;other&quot;</span> <span class="token keyword">end</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test4
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+------------+-----------------------------------------------------------------------------------+
| Time|root.test4.x|CASE WHEN root.test4.x = 1 THEN &quot;one&quot; WHEN root.test4.x = 2 THEN &quot;two&quot; ELSE &quot;other&quot;|
+-----------------------------+------------+-----------------------------------------------------------------------------------+
|1970-01-01T08:00:00.001+08:00| 1.0| one|
|1970-01-01T08:00:00.002+08:00| 2.0| two|
|1970-01-01T08:00:00.003+08:00| 3.0| other|
|1970-01-01T08:00:00.004+08:00| 4.0| other|
+-----------------------------+------------+-----------------------------------------------------------------------------------+
</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><h5 id="示例5-结果子句类型" tabindex="-1"><a class="header-anchor" href="#示例5-结果子句类型" aria-hidden="true">#</a> 示例5：结果子句类型</h5><p>CASE表达式的结果子句的返回值需要满足一定的类型限制。</p><p>此示例中，继续使用示例4中的数据。</p><h6 id="非法-boolean与其它类型共存" tabindex="-1"><a class="header-anchor" href="#非法-boolean与其它类型共存" aria-hidden="true">#</a> 非法：BOOLEAN与其它类型共存</h6><p>SQL语句：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> x<span class="token punctuation">,</span> <span class="token keyword">case</span> x <span class="token keyword">when</span> <span class="token number">1</span> <span class="token keyword">then</span> <span class="token boolean">true</span> <span class="token keyword">when</span> <span class="token number">2</span> <span class="token keyword">then</span> <span class="token number">2</span> <span class="token keyword">end</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test4
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>Msg: 701: CASE expression: BOOLEAN and other types cannot exist at same time
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><h6 id="合法-只存在boolean类型" tabindex="-1"><a class="header-anchor" href="#合法-只存在boolean类型" aria-hidden="true">#</a> 合法：只存在BOOLEAN类型</h6><p>SQL语句：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> x<span class="token punctuation">,</span> <span class="token keyword">case</span> x <span class="token keyword">when</span> <span class="token number">1</span> <span class="token keyword">then</span> <span class="token boolean">true</span> <span class="token keyword">when</span> <span class="token number">2</span> <span class="token keyword">then</span> <span class="token boolean">false</span> <span class="token keyword">end</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>result<span class="token punctuation">`</span></span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test4
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+------------+------+
| Time|root.test4.x|result|
+-----------------------------+------------+------+
|1970-01-01T08:00:00.001+08:00| 1.0| true|
|1970-01-01T08:00:00.002+08:00| 2.0| false|
|1970-01-01T08:00:00.003+08:00| 3.0| null|
|1970-01-01T08:00:00.004+08:00| 4.0| null|
+-----------------------------+------------+------+
</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><h6 id="非法-text与其它类型共存" tabindex="-1"><a class="header-anchor" href="#非法-text与其它类型共存" aria-hidden="true">#</a> 非法：TEXT与其它类型共存</h6><p>SQL语句：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> x<span class="token punctuation">,</span> <span class="token keyword">case</span> x <span class="token keyword">when</span> <span class="token number">1</span> <span class="token keyword">then</span> <span class="token number">1</span> <span class="token keyword">when</span> <span class="token number">2</span> <span class="token keyword">then</span> <span class="token string">&quot;str&quot;</span> <span class="token keyword">end</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>test4
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>Msg: 701: CASE expression: TEXT and other types cannot exist at same time
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><h6 id="合法-只存在text类型" tabindex="-1"><a class="header-anchor" href="#合法-只存在text类型" aria-hidden="true">#</a> 合法：只存在TEXT类型</h6><p>见示例1。</p><h6 id="合法-数值类型共存" tabindex="-1"><a class="header-anchor" href="#合法-数值类型共存" aria-hidden="true">#</a> 合法：数值类型共存</h6><p>SQL语句：</p><div class="language-sql line-numbers-mode" data-ext="sql"><pre class="language-sql"><code><span class="token keyword">select</span> x<span class="token punctuation">,</span> <span class="token keyword">case</span> x
<span class="token keyword">when</span> <span class="token number">1</span> <span class="token keyword">then</span> <span class="token number">1</span>
<span class="token keyword">when</span> <span class="token number">2</span> <span class="token keyword">then</span> <span class="token number">222222222222222</span>
<span class="token keyword">when</span> <span class="token number">3</span> <span class="token keyword">then</span> <span class="token number">3.3</span>
<span class="token keyword">when</span> <span class="token number">4</span> <span class="token keyword">then</span> <span class="token number">4.4444444444444</span>
<span class="token keyword">end</span> <span class="token keyword">as</span> <span class="token identifier"><span class="token punctuation">`</span>result<span class="token punctuation">`</span></span>
<span class="token keyword">from</span> root<span class="token punctuation">.</span>test4
</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>输出：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>+-----------------------------+------------+-------------------+
| Time|root.test4.x| result|
+-----------------------------+------------+-------------------+
|1970-01-01T08:00:00.001+08:00| 1.0| 1.0|
|1970-01-01T08:00:00.002+08:00| 2.0|2.22222222222222E14|
|1970-01-01T08:00:00.003+08:00| 3.0| 3.299999952316284|
|1970-01-01T08:00:00.004+08:00| 4.0| 4.44444465637207|
+-----------------------------+------------+-------------------+
</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></div><!----><footer class="page-meta"><div class="meta-item edit-link"><a href="https://github.com/apache/iotdb/edit/rel/1.2/docs/zh/UserGuide/Operators-Functions/Conditional.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/V1.2.x/Operators-Functions/Lambda.html" class="nav-link prev" aria-label="Lambda 表达式"><div class="hint"><span class="arrow start"></span>上一页</div><div class="link"><!---->Lambda 表达式</div></a><a href="/zh/UserGuide/V1.2.x/Operators-Functions/Data-Profiling.html" class="nav-link next" aria-label="数据画像"><div class="hint">下一页<span class="arrow end"></span></div><div class="link">数据画像<!----></div></a></nav><!----><!----><!--]--></main><!--]--><footer style="padding-bottom:2rem;"><span id="doc-version" style="display:none;">rel/1.2</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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