magento-test/app/code/Magento/MediaContent/etc/db_schema.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="media_content_asset" resource="default" engine="innodb" comment="Relation between media content and media asset">
        <column xsi:type="int" name="asset_id" unsigned="true" nullable="false" comment="Entity ID"/>
        <column xsi:type="varchar" length="255" name="entity_type" nullable="false" comment="Content type"/>
        <column xsi:type="varchar" length="255" name="entity_id" nullable="false" comment="Content entity id"/>
        <column xsi:type="varchar" length="255" name="field" nullable="false" comment="Content field"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="entity_type"/>
            <column name="entity_id"/>
            <column name="field"/>
            <column name="asset_id"/>
        </constraint>
        <index referenceId="MEDIA_CONTENT_ASSET_ASSET_ID" indexType="btree">
            <column name="asset_id"/>
        </index>
    </table>
</schema>