All Submissions:

• Have you followed the WooCommerce Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

We have decided to use placeholder entries in the posts table as the mechanism to prevent posts/orders id conflicts (#32086 (comment)), so this pull request implements the required changes:

• The post_id column is removed from the orders table.
  • The column is removed from the schema, but no database migration is provided to remove it if the table already exists. That's because the feature is in early stages of development and few people outside Automattic will have created the orders table already. Also the column continuing to be in place isn't harmful in any way.
• The SQL queries used to count the out of sync orders and to get the ids of these orders are adjusted according to the new mechanism.

Note: All the tests in WPPostToCOTMigratorTest are temporarily skipped because the tested code is still not adapted to the removal of the post_id column; they need to be "de-skipped" after (or as part of) #32700.

Closes #32663.
Closes #32665.

How to test the changes in this Pull Request:

Same testing instructions as in #32062. However, the SQL queries that create data for testing are now these (note that this time data needs to be created both in the new orders table and in the posts table):

/* Create some synchronized entries in orders table from existing orders in posts table */
INSERT INTO wp_wc_orders (id,date_created_gmt,date_updated_gmt)
SELECT ID,post_date_gmt,post_modified_gmt from wp_posts 
WHERE post_type='shop_order' AND post_status != 'auto-draft'
ORDER BY id DESC LIMIT 10;

/* Force some of the synchronized entries to be out of sync */
UPDATE wp_wc_orders SET date_updated_gmt=now() LIMIT 2;

/* Create some placeholder entries in posts table and the corresponding authotitative entries in the orders table
(LIMIT in second INSERT should be equal to the number of VALUES rows in the first INSERT)*/
INSERT INTO wp_posts (post_author,post_date,post_date_gmt,post_content,post_title,post_excerpt,post_status,comment_status,ping_status,post_password,post_name,to_ping,pinged,post_modified,post_modified_gmt,post_content_filtered,post_parent,guid,menu_order,post_type,post_mime_type,comment_count)
VALUES
(1,current_timestamp(),current_timestamp(),'','','','','','','','','','',current_timestamp(),current_timestamp(),'',0,'',0,('shop_order_placehold'),'',0),
(1,current_timestamp(),current_timestamp(),'','','','','','','','','','',current_timestamp(),current_timestamp(),'',0,'',0,('shop_order_placehold'),'',0),
(1,current_timestamp(),current_timestamp(),'','','','','','','','','','',current_timestamp(),current_timestamp(),'',0,'',0,('shop_order_placehold'),'',0),
(1,current_timestamp(),current_timestamp(),'','','','','','','','','','',current_timestamp(),current_timestamp(),'',0,'',0,('shop_order_placehold'),'',0);

INSERT INTO wp_wc_orders (id,date_created_gmt,date_updated_gmt)
SELECT ID,current_timestamp()+10,current_timestamp()+10 from wp_posts 
ORDER BY id DESC LIMIT 4;

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Have you created a changelog file by running pnpm nx affected --target=changelog?

FOR PR REVIEWER ONLY:

• I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.