# ClickHouse Reverse ETL Source

<p>You can now sync SQL audiences from ClickHouse with the <a href="https://www.rudderstack.com/docs/sources/reverse-etl/clickhouse/" >ClickHouse Reverse ETL Source</a>. Connect ClickHouse in <a href="https://www.rudderstack.com/docs/activate/lookout/" >Rudder Lookout</a>, build an audience, and activate it to a destination. Lookout automatically creates the source in your linked RudderStack workspace when you activate the audience.</p>

<blockquote class="announcement">
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    <div class="tip-text"><p><strong>The ClickHouse Reverse ETL Source is in Private Beta.</strong></p>
<p>Reach out to <a href="mailto:support@rudderstack.com" >Customer Success</a> to enable it for your workspace.</p>
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</blockquote>

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<h2 id="key-features">Key features</h2><ul>
<li><strong>SQL audiences in mirror mode</strong>: Build the audience in Lookout and activate it to a destination.</li>
<li><strong>Read-only access to your tables</strong>: RudderStack reads the rows your audience selects and writes only to a separate <code>_rudderstack</code> database, where it keeps snapshots and sync state.</li>
<li><strong>Diffs computed in ClickHouse</strong>: Each sync snapshots the current audience on your server and compares it with the previous snapshot. A normal sync sends removed members, then changed members, then new members.</li>
<li><strong>ClickHouse Cloud or a single node</strong>: Connect ClickHouse Cloud, including a service with several replicas, or a self-hosted server on one node. The server must run version 26.3 or later and accept HTTPS on a public address.</li>
</ul>
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<h2 id="get-started">Get started</h2><p>A Lookout admin adds the warehouse connection.</p>
<ol>
<li>Reach out to Customer Success to enable the ClickHouse source for your workspace. Then, follow <a href="https://www.rudderstack.com/docs/activate/lookout/integrations/rudderstack/" >How to Connect Your RudderStack Workspace to Lookout</a>.</li>
<li>In Lookout, go to <strong>Settings</strong> &gt; <strong>Warehouses</strong>, click <strong>Add account</strong>, and select <strong>ClickHouse</strong>.</li>
<li>Enter the connection settings. Check the <strong>Setup SQL</strong> under the form, and ask a ClickHouse administrator to run it if they haven&rsquo;t already.</li>
<li>Click <strong>Validate and create</strong>.</li>
<li>Build an audience on the ClickHouse connection and activate it to a destination.</li>
</ol>
<p>See the <a href="https://www.rudderstack.com/docs/sources/reverse-etl/clickhouse/" >ClickHouse Reverse ETL Source</a> for the grant script, connection settings, and what you can sync.</p>
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<h2 id="resources">Resources</h2><ul>
<li><a href="https://www.rudderstack.com/docs/sources/reverse-etl/clickhouse/#granting-permissions" >Grant permissions</a>: The user, the <code>_rudderstack</code> database, and the grants each sync needs</li>
<li><a href="https://www.rudderstack.com/docs/activate/lookout/audiences/build-an-audience/" >How to Build an Audience with the Agent</a>: Build the audience on your ClickHouse connection</li>
<li><a href="https://www.rudderstack.com/docs/activate/lookout/audiences/activate-an-audience/" >How to Activate an Audience to a Destination</a>: Send the audience to a destination and start the sync</li>
</ul>