create table magento 2
<?xml version="1.0"?>
<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
<table name="acme_ponumber_sales_order" engine="innodb" comment="Sales orders">
<!-- The standard auto-incrementing id of the table. -->
<column xsi:type="int" name="id" padding="10" unsigned="true" nullable="false" identity="true" comment="Id"/>
<!-- The reference to the order id. -->
<column xsi:type="int" name="order_id" padding="10" unsigned="true" nullable="false" comment="Order id"/>
<!-- The column we want to create is a free-form text field for a PO Number. -->
<column xsi:type="text" name="po_number" comment="Po number"/>
<!-- This is the primary key constraint for the database table. -->
<constraint xsi:type="primary" referenceId="PRIMARY">
<column name="id"/>
</constraint>
<!-- Create a foreign key constraint to the related table to be related, which in this case is sales_order. -->
<constraint xsi:type="foreign" referenceId="ACME_PONUMBER_SALES_ORDER_ORDER_ID_SALES_ORDER_ENTITY_ID" table="acme_ponumber_sales_order" column="order_id" referenceTable="sales_order" referenceColumn="entity_id" onDelete="CASCADE"/>
</table>
</schema>