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<h1 id="scan-query">Scan query</h1>
<p>Scan query returns raw Apache Druid (incubating) rows in streaming mode.</p>
<div class="highlight"><pre><code class="language-json" data-lang="json"><span></span> <span class="p">{</span>
<span class="nt">&quot;queryType&quot;</span><span class="p">:</span> <span class="s2">&quot;scan&quot;</span><span class="p">,</span>
<span class="nt">&quot;dataSource&quot;</span><span class="p">:</span> <span class="s2">&quot;wikipedia&quot;</span><span class="p">,</span>
<span class="nt">&quot;resultFormat&quot;</span><span class="p">:</span> <span class="s2">&quot;list&quot;</span><span class="p">,</span>
<span class="nt">&quot;columns&quot;</span><span class="p">:[],</span>
<span class="nt">&quot;intervals&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="s2">&quot;2013-01-01/2013-01-02&quot;</span>
<span class="p">],</span>
<span class="nt">&quot;batchSize&quot;</span><span class="p">:</span><span class="mi">20480</span><span class="p">,</span>
<span class="nt">&quot;limit&quot;</span><span class="p">:</span><span class="mi">5</span>
<span class="p">}</span>
</code></pre></div>
<p>There are several main parts to a scan query:</p>
<table><thead>
<tr>
<th>property</th>
<th>description</th>
<th>required?</th>
</tr>
</thead><tbody>
<tr>
<td>queryType</td>
<td>This String should always be &quot;scan&quot;; this is the first thing Druid looks at to figure out how to interpret the query</td>
<td>yes</td>
</tr>
<tr>
<td>dataSource</td>
<td>A String or Object defining the data source to query, very similar to a table in a relational database. See <a href="../querying/datasource.html">DataSource</a> for more information.</td>
<td>yes</td>
</tr>
<tr>
<td>intervals</td>
<td>A JSON Object representing ISO-8601 Intervals. This defines the time ranges to run the query over.</td>
<td>yes</td>
</tr>
<tr>
<td>resultFormat</td>
<td>How result represented, list or compactedList or valueVector. Currently only <code>list</code> and <code>compactedList</code> are supported. Default is <code>list</code></td>
<td>no</td>
</tr>
<tr>
<td>filter</td>
<td>See <a href="../querying/filters.html">Filters</a></td>
<td>no</td>
</tr>
<tr>
<td>columns</td>
<td>A String array of dimensions and metrics to scan. If left empty, all dimensions and metrics are returned.</td>
<td>no</td>
</tr>
<tr>
<td>batchSize</td>
<td>How many rows buffered before return to client. Default is <code>20480</code></td>
<td>no</td>
</tr>
<tr>
<td>limit</td>
<td>How many rows to return. If not specified, all rows will be returned.</td>
<td>no</td>
</tr>
<tr>
<td>legacy</td>
<td>Return results consistent with the legacy &quot;scan-query&quot; contrib extension. Defaults to the value set by <code>druid.query.scan.legacy</code>, which in turn defaults to false. See <a href="#legacy-mode">Legacy mode</a> for details.</td>
<td>no</td>
</tr>
<tr>
<td>context</td>
<td>An additional JSON Object which can be used to specify certain flags.</td>
<td>no</td>
</tr>
</tbody></table>
<h2 id="example-results">Example results</h2>
<p>The format of the result when resultFormat equals to <code>list</code>:</p>
<div class="highlight"><pre><code class="language-json" data-lang="json"><span></span> <span class="p">[{</span>
<span class="nt">&quot;segmentId&quot;</span> <span class="p">:</span> <span class="s2">&quot;wikipedia_editstream_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9&quot;</span><span class="p">,</span>
<span class="nt">&quot;columns&quot;</span> <span class="p">:</span> <span class="p">[</span>
<span class="s2">&quot;timestamp&quot;</span><span class="p">,</span>
<span class="s2">&quot;robot&quot;</span><span class="p">,</span>
<span class="s2">&quot;namespace&quot;</span><span class="p">,</span>
<span class="s2">&quot;anonymous&quot;</span><span class="p">,</span>
<span class="s2">&quot;unpatrolled&quot;</span><span class="p">,</span>
<span class="s2">&quot;page&quot;</span><span class="p">,</span>
<span class="s2">&quot;language&quot;</span><span class="p">,</span>
<span class="s2">&quot;newpage&quot;</span><span class="p">,</span>
<span class="s2">&quot;user&quot;</span><span class="p">,</span>
<span class="s2">&quot;count&quot;</span><span class="p">,</span>
<span class="s2">&quot;added&quot;</span><span class="p">,</span>
<span class="s2">&quot;delta&quot;</span><span class="p">,</span>
<span class="s2">&quot;variation&quot;</span><span class="p">,</span>
<span class="s2">&quot;deleted&quot;</span>
<span class="p">],</span>
<span class="nt">&quot;events&quot;</span> <span class="p">:</span> <span class="p">[</span> <span class="p">{</span>
<span class="nt">&quot;timestamp&quot;</span> <span class="p">:</span> <span class="s2">&quot;2013-01-01T00:00:00.000Z&quot;</span><span class="p">,</span>
<span class="nt">&quot;robot&quot;</span> <span class="p">:</span> <span class="s2">&quot;1&quot;</span><span class="p">,</span>
<span class="nt">&quot;namespace&quot;</span> <span class="p">:</span> <span class="s2">&quot;article&quot;</span><span class="p">,</span>
<span class="nt">&quot;anonymous&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;unpatrolled&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;page&quot;</span> <span class="p">:</span> <span class="s2">&quot;11._korpus_(NOVJ)&quot;</span><span class="p">,</span>
<span class="nt">&quot;language&quot;</span> <span class="p">:</span> <span class="s2">&quot;sl&quot;</span><span class="p">,</span>
<span class="nt">&quot;newpage&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;user&quot;</span> <span class="p">:</span> <span class="s2">&quot;EmausBot&quot;</span><span class="p">,</span>
<span class="nt">&quot;count&quot;</span> <span class="p">:</span> <span class="mf">1.0</span><span class="p">,</span>
<span class="nt">&quot;added&quot;</span> <span class="p">:</span> <span class="mf">39.0</span><span class="p">,</span>
<span class="nt">&quot;delta&quot;</span> <span class="p">:</span> <span class="mf">39.0</span><span class="p">,</span>
<span class="nt">&quot;variation&quot;</span> <span class="p">:</span> <span class="mf">39.0</span><span class="p">,</span>
<span class="nt">&quot;deleted&quot;</span> <span class="p">:</span> <span class="mf">0.0</span>
<span class="p">},</span> <span class="p">{</span>
<span class="nt">&quot;timestamp&quot;</span> <span class="p">:</span> <span class="s2">&quot;2013-01-01T00:00:00.000Z&quot;</span><span class="p">,</span>
<span class="nt">&quot;robot&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;namespace&quot;</span> <span class="p">:</span> <span class="s2">&quot;article&quot;</span><span class="p">,</span>
<span class="nt">&quot;anonymous&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;unpatrolled&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;page&quot;</span> <span class="p">:</span> <span class="s2">&quot;112_U.S._580&quot;</span><span class="p">,</span>
<span class="nt">&quot;language&quot;</span> <span class="p">:</span> <span class="s2">&quot;en&quot;</span><span class="p">,</span>
<span class="nt">&quot;newpage&quot;</span> <span class="p">:</span> <span class="s2">&quot;1&quot;</span><span class="p">,</span>
<span class="nt">&quot;user&quot;</span> <span class="p">:</span> <span class="s2">&quot;MZMcBride&quot;</span><span class="p">,</span>
<span class="nt">&quot;count&quot;</span> <span class="p">:</span> <span class="mf">1.0</span><span class="p">,</span>
<span class="nt">&quot;added&quot;</span> <span class="p">:</span> <span class="mf">70.0</span><span class="p">,</span>
<span class="nt">&quot;delta&quot;</span> <span class="p">:</span> <span class="mf">70.0</span><span class="p">,</span>
<span class="nt">&quot;variation&quot;</span> <span class="p">:</span> <span class="mf">70.0</span><span class="p">,</span>
<span class="nt">&quot;deleted&quot;</span> <span class="p">:</span> <span class="mf">0.0</span>
<span class="p">},</span> <span class="p">{</span>
<span class="nt">&quot;timestamp&quot;</span> <span class="p">:</span> <span class="s2">&quot;2013-01-01T00:00:00.000Z&quot;</span><span class="p">,</span>
<span class="nt">&quot;robot&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;namespace&quot;</span> <span class="p">:</span> <span class="s2">&quot;article&quot;</span><span class="p">,</span>
<span class="nt">&quot;anonymous&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;unpatrolled&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;page&quot;</span> <span class="p">:</span> <span class="s2">&quot;113_U.S._243&quot;</span><span class="p">,</span>
<span class="nt">&quot;language&quot;</span> <span class="p">:</span> <span class="s2">&quot;en&quot;</span><span class="p">,</span>
<span class="nt">&quot;newpage&quot;</span> <span class="p">:</span> <span class="s2">&quot;1&quot;</span><span class="p">,</span>
<span class="nt">&quot;user&quot;</span> <span class="p">:</span> <span class="s2">&quot;MZMcBride&quot;</span><span class="p">,</span>
<span class="nt">&quot;count&quot;</span> <span class="p">:</span> <span class="mf">1.0</span><span class="p">,</span>
<span class="nt">&quot;added&quot;</span> <span class="p">:</span> <span class="mf">77.0</span><span class="p">,</span>
<span class="nt">&quot;delta&quot;</span> <span class="p">:</span> <span class="mf">77.0</span><span class="p">,</span>
<span class="nt">&quot;variation&quot;</span> <span class="p">:</span> <span class="mf">77.0</span><span class="p">,</span>
<span class="nt">&quot;deleted&quot;</span> <span class="p">:</span> <span class="mf">0.0</span>
<span class="p">},</span> <span class="p">{</span>
<span class="nt">&quot;timestamp&quot;</span> <span class="p">:</span> <span class="s2">&quot;2013-01-01T00:00:00.000Z&quot;</span><span class="p">,</span>
<span class="nt">&quot;robot&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;namespace&quot;</span> <span class="p">:</span> <span class="s2">&quot;article&quot;</span><span class="p">,</span>
<span class="nt">&quot;anonymous&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;unpatrolled&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;page&quot;</span> <span class="p">:</span> <span class="s2">&quot;113_U.S._73&quot;</span><span class="p">,</span>
<span class="nt">&quot;language&quot;</span> <span class="p">:</span> <span class="s2">&quot;en&quot;</span><span class="p">,</span>
<span class="nt">&quot;newpage&quot;</span> <span class="p">:</span> <span class="s2">&quot;1&quot;</span><span class="p">,</span>
<span class="nt">&quot;user&quot;</span> <span class="p">:</span> <span class="s2">&quot;MZMcBride&quot;</span><span class="p">,</span>
<span class="nt">&quot;count&quot;</span> <span class="p">:</span> <span class="mf">1.0</span><span class="p">,</span>
<span class="nt">&quot;added&quot;</span> <span class="p">:</span> <span class="mf">70.0</span><span class="p">,</span>
<span class="nt">&quot;delta&quot;</span> <span class="p">:</span> <span class="mf">70.0</span><span class="p">,</span>
<span class="nt">&quot;variation&quot;</span> <span class="p">:</span> <span class="mf">70.0</span><span class="p">,</span>
<span class="nt">&quot;deleted&quot;</span> <span class="p">:</span> <span class="mf">0.0</span>
<span class="p">},</span> <span class="p">{</span>
<span class="nt">&quot;timestamp&quot;</span> <span class="p">:</span> <span class="s2">&quot;2013-01-01T00:00:00.000Z&quot;</span><span class="p">,</span>
<span class="nt">&quot;robot&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;namespace&quot;</span> <span class="p">:</span> <span class="s2">&quot;article&quot;</span><span class="p">,</span>
<span class="nt">&quot;anonymous&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;unpatrolled&quot;</span> <span class="p">:</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span>
<span class="nt">&quot;page&quot;</span> <span class="p">:</span> <span class="s2">&quot;113_U.S._756&quot;</span><span class="p">,</span>
<span class="nt">&quot;language&quot;</span> <span class="p">:</span> <span class="s2">&quot;en&quot;</span><span class="p">,</span>
<span class="nt">&quot;newpage&quot;</span> <span class="p">:</span> <span class="s2">&quot;1&quot;</span><span class="p">,</span>
<span class="nt">&quot;user&quot;</span> <span class="p">:</span> <span class="s2">&quot;MZMcBride&quot;</span><span class="p">,</span>
<span class="nt">&quot;count&quot;</span> <span class="p">:</span> <span class="mf">1.0</span><span class="p">,</span>
<span class="nt">&quot;added&quot;</span> <span class="p">:</span> <span class="mf">68.0</span><span class="p">,</span>
<span class="nt">&quot;delta&quot;</span> <span class="p">:</span> <span class="mf">68.0</span><span class="p">,</span>
<span class="nt">&quot;variation&quot;</span> <span class="p">:</span> <span class="mf">68.0</span><span class="p">,</span>
<span class="nt">&quot;deleted&quot;</span> <span class="p">:</span> <span class="mf">0.0</span>
<span class="p">}</span> <span class="p">]</span>
<span class="p">}</span> <span class="p">]</span>
</code></pre></div>
<p>The format of the result when resultFormat equals to <code>compactedList</code>:</p>
<div class="highlight"><pre><code class="language-json" data-lang="json"><span></span> <span class="p">[{</span>
<span class="nt">&quot;segmentId&quot;</span> <span class="p">:</span> <span class="s2">&quot;wikipedia_editstream_2012-12-29T00:00:00.000Z_2013-01-10T08:00:00.000Z_2013-01-10T08:13:47.830Z_v9&quot;</span><span class="p">,</span>
<span class="nt">&quot;columns&quot;</span> <span class="p">:</span> <span class="p">[</span>
<span class="s2">&quot;timestamp&quot;</span><span class="p">,</span> <span class="s2">&quot;robot&quot;</span><span class="p">,</span> <span class="s2">&quot;namespace&quot;</span><span class="p">,</span> <span class="s2">&quot;anonymous&quot;</span><span class="p">,</span> <span class="s2">&quot;unpatrolled&quot;</span><span class="p">,</span> <span class="s2">&quot;page&quot;</span><span class="p">,</span> <span class="s2">&quot;language&quot;</span><span class="p">,</span> <span class="s2">&quot;newpage&quot;</span><span class="p">,</span> <span class="s2">&quot;user&quot;</span><span class="p">,</span> <span class="s2">&quot;count&quot;</span><span class="p">,</span> <span class="s2">&quot;added&quot;</span><span class="p">,</span> <span class="s2">&quot;delta&quot;</span><span class="p">,</span> <span class="s2">&quot;variation&quot;</span><span class="p">,</span> <span class="s2">&quot;deleted&quot;</span>
<span class="p">],</span>
<span class="nt">&quot;events&quot;</span> <span class="p">:</span> <span class="p">[</span>
<span class="p">[</span><span class="s2">&quot;2013-01-01T00:00:00.000Z&quot;</span><span class="p">,</span> <span class="s2">&quot;1&quot;</span><span class="p">,</span> <span class="s2">&quot;article&quot;</span><span class="p">,</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span> <span class="s2">&quot;11._korpus_(NOVJ)&quot;</span><span class="p">,</span> <span class="s2">&quot;sl&quot;</span><span class="p">,</span> <span class="s2">&quot;0&quot;</span><span class="p">,</span> <span class="s2">&quot;EmausBot&quot;</span><span class="p">,</span> <span class="mf">1.0</span><span class="p">,</span> <span class="mf">39.0</span><span class="p">,</span> <span class="mf">39.0</span><span class="p">,</span> <span class="mf">39.0</span><span class="p">,</span> <span class="mf">0.0</span><span class="p">],</span>
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<span class="p">]</span>
<span class="p">}</span> <span class="p">]</span>
</code></pre></div>
<p>The biggest difference between select query and scan query is that, scan query doesn&#39;t retain all rows in memory before rows can be returned to client.<br>
It will cause memory pressure if too many rows required by select query.<br>
Scan query doesn&#39;t have this issue.<br>
Scan query can return all rows without issuing another pagination query, which is extremely useful when query against Historical or realtime process directly.</p>
<h2 id="legacy-mode">Legacy mode</h2>
<p>The Scan query supports a legacy mode designed for protocol compatibility with the former scan-query contrib extension.
In legacy mode you can expect the following behavior changes:</p>
<ul>
<li>The <strong>time column is returned as &quot;timestamp&quot; rather than &quot;</strong>time&quot;. This will take precedence over any other column
you may have that is named &quot;timestamp&quot;.</li>
<li>The __time column is included in the list of columns even if you do not specifically ask for it.</li>
<li>Timestamps are returned as ISO8601 time strings rather than integers (milliseconds since 1970-01-01 00:00:00 UTC).</li>
</ul>
<p>Legacy mode can be triggered either by passing <code>&quot;legacy&quot; : true</code> in your query JSON, or by setting
<code>druid.query.scan.legacy = true</code> on your Druid processes. If you were previously using the scan-query contrib extension,
the best way to migrate is to activate legacy mode during a rolling upgrade, then switch it off after the upgrade
is complete.</p>
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