Why is the column in the table not deleted when db_schema.xml is changed?

Question

Magento

Described the table in a declarative schema (Magento 2.3):
app/code/Mi/DeclarativeSchema/etc/db_schema.xml

<?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="mi_declarative_schema_test" resource="default" comment="Declarative schema test">
        <column xsi:type="int" name="id" identity="true" comment="ID Auto Increment" />
        <column xsi:type="varchar" name="name" length="1024" nullable="false" comment="Name" />
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id" />
        </constraint>
    </table>
</schema>

Made setup:upgrade, the table was created, everything is OK. I add columns, I do an upgrade - they are added. But when I delete columns from xml, they are not deleted in the table.
Here https://devdocs.magento.com/guides/v2.3/extension-... it is written that it is enough to simply delete or comment out the column line.
Magento connects to the database as root.

Answer 1

Try it like I did:
1) create a db_schema.xml file with the following structure:

<?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="mi_declarative_schema_new" resource="default" comment="Declarative schema test">
        <column xsi:type="int" name="id" identity="true" comment="ID Auto Increment" />
        <column xsi:type="text" name="name" comment="name" />
        <column xsi:type="text" name="email" comment="email" />
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id" />
        </constraint>
    </table>
</schema>

2) Clear cache php bin/magento cache:flush
3) Generate db_schema_whitelist.json file using command

php bin/magento setup:db-declaration:generate-whitelist --module-name=Mi_DeclarativeSchema

3) Run upgrade php bin/magento setup:upgrade
After that, a new table will be created with the columns that we specified:
4) Next, comment out the column we don't need:

<?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="mi_declarative_schema_new" resource="default" comment="Declarative schema test">
        <column xsi:type="int" name="id" identity="true" comment="ID Auto Increment" />
        <column xsi:type="text" name="name" comment="name" />
        <!--<column xsi:type="text" name="email" comment="email" />-->
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id" />
        </constraint>
    </table>

5) clear the cache just in case
6) run the whitelist generation again.

php bin/magento setup:db-declaration:generate-whitelist --module-name=Mi_DeclarativeSchema

7) now we run upgrade
and voila , our column has been deleted:
The bottom line is that you need to generate a whitelist after each change in the database, you can read more about this in the documentation. But this is a temporary solution (whitelist) and there will be something new soon, but for now, like this.