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class="search-icon" tabindex="0"></span><input type="search" id="search_input_react" placeholder="Loading..." aria-label="Search" class="navbar__search-input search-bar" disabled=""></div></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div id="__docusaurus_skipToContent_fallback" class="main-wrapper mainWrapper_z2l0 docsWrapper_BCFX"><button aria-label="Scroll back to top" class="clean-btn theme-back-to-top-button backToTopButton_sjWU" type="button"></button><div class="docPage__5DB"><main class="docMainContainer_gTbr docMainContainerEnhanced_Uz_u"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Cardinality/HyperUnique aggregators</h1></header><h2 class="anchor anchorWithStickyNavbar_LWe7" id="cardinality-aggregator">Cardinality aggregator<a href="#cardinality-aggregator" class="hash-link" aria-label="Direct link to Cardinality aggregator" title="Direct link to Cardinality aggregator"></a></h2><p>Computes the cardinality of a set of Apache Druid dimensions, using HyperLogLog to estimate the cardinality. Please note that this
 aggregator will be much slower than indexing a column with the hyperUnique aggregator. This aggregator also runs over a dimension column, which
 means the string dimension cannot be removed from the dataset to improve rollup. In general, we strongly recommend using the hyperUnique aggregator
 instead of the cardinality aggregator if you do not care about the individual values of a dimension.</p><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;cardinality&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;name&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;&lt;output_name&gt;&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;fields&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">[</span><span class="token plain"> &lt;dimension1&gt;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> &lt;dimension2&gt;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> ... </span><span class="token punctuation" style="color:rgb(199, 146, 234)">]</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;byRow&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> &lt;</span><span class="token boolean" style="color:rgb(255, 88, 116)">false</span><span class="token plain"> | </span><span class="token boolean" style="color:rgb(255, 88, 116)">true</span><span class="token plain">&gt; # (optional</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> defaults to </span><span class="token boolean" style="color:rgb(255, 88, 116)">false</span><span class="token plain">)</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;round&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> &lt;</span><span class="token boolean" style="color:rgb(255, 88, 116)">false</span><span class="token plain"> | </span><span class="token boolean" style="color:rgb(255, 88, 116)">true</span><span class="token plain">&gt; # (optional</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> defaults to </span><span class="token boolean" style="color:rgb(255, 88, 116)">false</span><span class="token plain">)</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>Each individual element of the &quot;fields&quot; list can be a String or <a href="/docs/32.0.0/querying/dimensionspecs">DimensionSpec</a>. A String dimension in the fields list is equivalent to a DefaultDimensionSpec (no transformations).</p><p>The HyperLogLog algorithm generates decimal estimates with some error. &quot;round&quot; can be set to true to round off estimated
 values to whole numbers. Note that even with rounding, the cardinality is still an estimate. The &quot;round&quot; field only
 affects query-time behavior, and is ignored at ingestion-time.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="cardinality-by-value">Cardinality by value<a href="#cardinality-by-value" class="hash-link" aria-label="Direct link to Cardinality by value" title="Direct link to Cardinality by value"></a></h3><p>When setting <code>byRow</code> to <code>false</code> (the default) it computes the cardinality of the set composed of the union of all dimension values for all the given dimensions.</p><ul><li>For a single dimension, this is equivalent to</li></ul><div class="language-sql codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-sql codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">SELECT</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">COUNT</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token keyword" style="font-style:italic">DISTINCT</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token plain">dimension</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">FROM</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">&lt;</span><span class="token plain">datasource</span><span class="token operator" style="color:rgb(137, 221, 255)">&gt;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><ul><li>For multiple dimensions, this is equivalent to something akin to</li></ul><div class="language-sql codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-sql codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">SELECT</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">COUNT</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token keyword" style="font-style:italic">DISTINCT</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token keyword" style="font-style:italic">value</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">FROM</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token keyword" style="font-style:italic">SELECT</span><span class="token plain"> dim_1 </span><span class="token keyword" style="font-style:italic">as</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">value</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">FROM</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">&lt;</span><span class="token plain">datasource</span><span class="token operator" style="color:rgb(137, 221, 255)">&gt;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token keyword" style="font-style:italic">UNION</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token keyword" style="font-style:italic">SELECT</span><span class="token plain"> dim_2 </span><span class="token keyword" style="font-style:italic">as</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">value</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">FROM</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">&lt;</span><span class="token plain">datasource</span><span class="token operator" style="color:rgb(137, 221, 255)">&gt;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token keyword" style="font-style:italic">UNION</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token keyword" style="font-style:italic">SELECT</span><span class="token plain"> dim_3 </span><span class="token keyword" style="font-style:italic">as</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">value</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">FROM</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">&lt;</span><span class="token plain">datasource</span><span class="token operator" style="color:rgb(137, 221, 255)">&gt;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h3 class="anchor anchorWithStickyNavbar_LWe7" id="cardinality-by-row">Cardinality by row<a href="#cardinality-by-row" class="hash-link" aria-label="Direct link to Cardinality by row" title="Direct link to Cardinality by row"></a></h3><p>When setting <code>byRow</code> to <code>true</code> it computes the cardinality by row, i.e. the cardinality of distinct dimension combinations.
 This is equivalent to something akin to</p><div class="language-sql codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-sql codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">SELECT</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">COUNT</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token operator" style="color:rgb(137, 221, 255)">*</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">FROM</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">SELECT</span><span class="token plain"> DIM1</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> DIM2</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> DIM3 </span><span class="token keyword" style="font-style:italic">FROM</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">&lt;</span><span class="token plain">datasource</span><span class="token operator" style="color:rgb(137, 221, 255)">&gt;</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">GROUP</span><span class="token plain"> </span><span class="token keyword" style="font-style:italic">BY</span><span class="token plain"> DIM1</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> DIM2</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> DIM3 </span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p><strong>Example</strong></p><p>Determine the number of distinct countries people are living in or have come from.</p><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;cardinality&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;name&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;distinct_countries&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;fields&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">[</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;country_of_origin&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;country_of_residence&quot;</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">]</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>Determine the number of distinct people (i.e. combinations of first and last name).</p><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;cardinality&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;name&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;distinct_people&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;fields&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">[</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;first_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;last_name&quot;</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">]</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;byRow&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token boolean" style="color:rgb(255, 88, 116)">true</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>Determine the number of distinct starting characters of last names</p><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;type&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;cardinality&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;name&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;distinct_last_name_first_char&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;fields&quot;</span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">[</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">    </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">     </span><span class="token property">&quot;type&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;extraction&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">     </span><span class="token property">&quot;dimension&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;last_name&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">     </span><span class="token property">&quot;outputName&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain">  </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;last_name_first_char&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">     </span><span class="token property">&quot;extractionFn&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"> </span><span class="token property">&quot;type&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;substring&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;index&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token number" style="color:rgb(247, 140, 108)">0</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> </span><span class="token property">&quot;length&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token number" style="color:rgb(247, 140, 108)">1</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">    </span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token punctuation" style="color:rgb(199, 146, 234)">]</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;byRow&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token boolean" style="color:rgb(255, 88, 116)">true</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="hyperunique-aggregator">HyperUnique aggregator<a href="#hyperunique-aggregator" class="hash-link" aria-label="Direct link to HyperUnique aggregator" title="Direct link to HyperUnique aggregator"></a></h2><p>Uses <a href="http://algo.inria.fr/flajolet/Publications/FlFuGaMe07.pdf" target="_blank" rel="noopener noreferrer">HyperLogLog</a> to compute the estimated cardinality of a dimension that has been aggregated as a &quot;hyperUnique&quot; metric at indexing time.</p><div class="language-json codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-json codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;type&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">&quot;hyperUnique&quot;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;name&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> &lt;output_name&gt;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;fieldName&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> &lt;metric_name&gt;</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;isInputHyperUnique&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token boolean" style="color:rgb(255, 88, 116)">false</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">  </span><span class="token property">&quot;round&quot;</span><span class="token plain"> </span><span class="token operator" style="color:rgb(137, 221, 255)">:</span><span class="token plain"> </span><span class="token boolean" style="color:rgb(255, 88, 116)">false</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>&quot;isInputHyperUnique&quot; can be set to true to index precomputed HLL (Base64 encoded output from druid-hll is expected).
 The &quot;isInputHyperUnique&quot; field only affects ingestion-time behavior, and is ignored at query-time.</p><p>The HyperLogLog algorithm generates decimal estimates with some error. &quot;round&quot; can be set to true to round off estimated
 values to whole numbers. Note that even with rounding, the cardinality is still an estimate. The &quot;round&quot; field only
 affects query-time behavior, and is ignored at ingestion-time.</p></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#cardinality-aggregator" class="table-of-contents__link toc-highlight">Cardinality aggregator</a><ul><li><a href="#cardinality-by-value" class="table-of-contents__link toc-highlight">Cardinality by value</a></li><li><a href="#cardinality-by-row" class="table-of-contents__link toc-highlight">Cardinality by row</a></li></ul></li><li><a href="#hyperunique-aggregator" class="table-of-contents__link toc-highlight">HyperUnique aggregator</a></li></ul></div></div></div></div></main></div></div><footer class="footer"><div class="container container-fluid"><div class="footer__bottom text--center"><div class="margin-bottom--sm"><img src="/img/favicon.png" class="themedImage_ToTc themedImage--light_HNdA footer__logo"><img src="/img/favicon.png" class="themedImage_ToTc themedImage--dark_i4oU footer__logo"></div><div class="footer__copyright">Copyright © 2023 Apache Software Foundation. Except where otherwise noted, licensed under CC BY-SA 4.0. Apache Druid, Druid, and the Druid logo are either registered trademarks or trademarks of The Apache Software Foundation in the United States and other countries.</div></div></div></footer></div>
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