<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Virtual columns · Apache Druid</title><meta name="viewport" content="width=device-width"/><link rel="canonical" href="https://druid.apache.org/docs/0.20.0/querying/virtual-columns.html"/><meta name="generator" content="Docusaurus"/><meta name="description" content="&lt;!--"/><meta name="docsearch:language" content="en"/><meta name="docsearch:version" content="0.20.0" /><meta property="og:title" content="Virtual columns · Apache Druid"/><meta property="og:type" content="website"/><meta property="og:url" content="https://druid.apache.org/index.html"/><meta property="og:description" content="&lt;!--"/><meta property="og:image" content="https://druid.apache.org/img/druid_nav.png"/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://druid.apache.org/img/druid_nav.png"/><link rel="shortcut icon" href="/img/favicon.png"/><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css"/><script async="" src="https://www.googletagmanager.com/gtag/js?id=UA-131010415-1"></script><script>
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href="/docs/0.20.0/querying/sql.html">Druid SQL</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/querying/querying.html">Native queries</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/querying/query-execution.html">Query execution</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Concepts</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.20.0/querying/datasource.html">Datasources</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/querying/joins.html">Joins</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/querying/lookups.html">Lookups</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/querying/multi-value-dimensions.html">Multi-value dimensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/querying/multitenancy.html">Multitenancy</a></li><li class="navListItem"><a class="navItem" 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href="/docs/0.20.0/operations/http-compression.html">HTTP compression</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/tls-support.html">TLS support</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/password-provider.html">Password providers</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/dump-segment.html">dump-segment tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/reset-cluster.html">reset-cluster tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/insert-segment-to-db.html">insert-segment-to-db tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/pull-deps.html">pull-deps tool</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Misc</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/management-uis.html">Legacy Management UIs</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/deep-storage-migration.html">Deep storage migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/export-metadata.html">Export Metadata Tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/metadata-migration.html">Metadata Migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/segment-optimization.html">Segment Size Optimization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/operations/use_sbt_to_build_fat_jar.html">Content for build.sbt</a></li></ul></div></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Development<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/overview.html">Developing on Druid</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/modules.html">Creating extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/javascript.html">JavaScript functionality</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/build.html">Build from source</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/versioning.html">Versioning</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/experimental.html">Experimental features</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Misc<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.20.0/misc/papers-and-talks.html">Papers</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Hidden<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.20.0/comparisons/druid-vs-elasticsearch.html">Apache Druid vs Elasticsearch</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/comparisons/druid-vs-key-value.html">Apache Druid vs. Key/Value Stores (HBase/Cassandra/OpenTSDB)</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/comparisons/druid-vs-kudu.html">Apache Druid vs Kudu</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/comparisons/druid-vs-redshift.html">Apache Druid vs Redshift</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/comparisons/druid-vs-spark.html">Apache Druid vs Spark</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/comparisons/druid-vs-sql-on-hadoop.html">Apache Druid vs SQL-on-Hadoop</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/auth.html">Authentication and Authorization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/broker.html">Broker</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/coordinator.html">Coordinator Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/historical.html">Historical Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/indexer.html">Indexer Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/indexing-service.html">Indexing Service</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/middlemanager.html">MiddleManager Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/overlord.html">Overlord Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/router.html">Router Process</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/design/peons.html">Peons</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/extensions-core/approximate-histograms.html">Approximate Histogram aggregators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/extensions-core/avro.html">Apache Avro</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/extensions-core/azure.html">Microsoft Azure</a></li><li class="navListItem"><a class="navItem" href="/docs/0.20.0/development/extensions-core/bloom-filter.html">Bloom Filter</a></li><li class="navListItem"><a class="navItem" 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<blockquote>
<p>Apache Druid supports two query languages: <a href="/docs/0.20.0/querying/sql.html">Druid SQL</a> and <a href="/docs/0.20.0/querying/querying.html">native queries</a>.
This document describes the native
language. For information about functions available in SQL, refer to the
<a href="/docs/0.20.0/querying/sql.html#scalar-functions">SQL documentation</a>.</p>
</blockquote>
<p>Virtual columns are queryable column &quot;views&quot; created from a set of columns during a query.</p>
<p>A virtual column can potentially draw from multiple underlying columns, although a virtual column always presents itself as a single column.</p>
<p>Virtual columns can be used as dimensions or as inputs to aggregators.</p>
<p>Each Apache Druid query can accept a list of virtual columns as a parameter. The following scan query is provided as an example:</p>
<pre><code class="hljs">{
 <span class="hljs-attr">"queryType"</span>: <span class="hljs-string">"scan"</span>,
 <span class="hljs-attr">"dataSource"</span>: <span class="hljs-string">"page_data"</span>,
 <span class="hljs-attr">"columns"</span>:[],
 <span class="hljs-attr">"virtualColumns"</span>: [
    {
      <span class="hljs-attr">"type"</span>: <span class="hljs-string">"expression"</span>,
      <span class="hljs-attr">"name"</span>: <span class="hljs-string">"fooPage"</span>,
      <span class="hljs-attr">"expression"</span>: <span class="hljs-string">"concat('foo' + page)"</span>,
      <span class="hljs-attr">"outputType"</span>: <span class="hljs-string">"STRING"</span>
    },
    {
      <span class="hljs-attr">"type"</span>: <span class="hljs-string">"expression"</span>,
      <span class="hljs-attr">"name"</span>: <span class="hljs-string">"tripleWordCount"</span>,
      <span class="hljs-attr">"expression"</span>: <span class="hljs-string">"wordCount * 3"</span>,
      <span class="hljs-attr">"outputType"</span>: <span class="hljs-string">"LONG"</span>
    }
  ],
 <span class="hljs-attr">"intervals"</span>: [
   <span class="hljs-string">"2013-01-01/2019-01-02"</span>
 ]
}
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="virtual-column-types"></a><a href="#virtual-column-types" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Virtual column types</h2>
<h3><a class="anchor" aria-hidden="true" id="expression-virtual-column"></a><a href="#expression-virtual-column" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Expression virtual column</h3>
<p>The expression virtual column has the following syntax:</p>
<pre><code class="hljs">{
  <span class="hljs-string">"type"</span>: <span class="hljs-string">"expression"</span>,
  <span class="hljs-string">"name"</span>: &lt;name of the virtual column&gt;,
  <span class="hljs-string">"expression"</span>: &lt;row expression&gt;,
  <span class="hljs-string">"outputType"</span>: &lt;output value<span class="hljs-built_in"> type </span>of expression&gt;
}
</code></pre>
<table>
<thead>
<tr><th>property</th><th>description</th><th>required?</th></tr>
</thead>
<tbody>
<tr><td>name</td><td>The name of the virtual column.</td><td>yes</td></tr>
<tr><td>expression</td><td>An <a href="/docs/0.20.0/misc/math-expr.html">expression</a> that takes a row as input and outputs a value for the virtual column.</td><td>yes</td></tr>
<tr><td>outputType</td><td>The expression's output will be coerced to this type. Can be LONG, FLOAT, DOUBLE, or STRING.</td><td>no, default is FLOAT</td></tr>
</tbody>
</table>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/0.20.0/querying/sorting-orders.html"><span class="arrow-prev">← </span><span>String comparators</span></a><a class="docs-next button" href="/docs/0.20.0/development/geo.html"><span>Spatial filters</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#virtual-column-types">Virtual column types</a><ul class="toc-headings"><li><a href="#expression-virtual-column">Expression virtual column</a></li></ul></li></ul></nav></div><footer class="nav-footer druid-footer" id="footer"><div class="container"><div class="text-center"><p><a href="/technology">Technology</a> · <a href="/use-cases">Use Cases</a> · <a href="/druid-powered">Powered by Druid</a> · <a href="/docs/0.20.0/latest">Docs</a> · <a href="/community/">Community</a> · <a href="/downloads.html">Download</a> · <a href="/faq">FAQ</a></p></div><div class="text-center"><a title="Join the user group" href="https://groups.google.com/forum/#!forum/druid-user" target="_blank"><span class="fa fa-comments"></span></a> · <a title="Follow Druid" href="https://twitter.com/druidio" target="_blank"><span class="fab fa-twitter"></span></a> · <a title="Download via Apache" href="https://www.apache.org/dyn/closer.cgi?path=/incubator/druid/{{ site.druid_versions[0].versions[0].version }}/apache-druid-{{ site.druid_versions[0].versions[0].version }}-bin.tar.gz" target="_blank"><span class="fas fa-feather"></span></a> · <a title="GitHub" href="https://github.com/apache/druid" target="_blank"><span class="fab fa-github"></span></a></div><div class="text-center license">Copyright © 2019 <a href="https://www.apache.org/" target="_blank">Apache Software Foundation</a>.<br/>Except where otherwise noted, licensed under <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0</a>.<br/>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></footer></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><script>
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