Delete Records Based on Conditions from Another Table

DELETE FROM
  users
WHERE
  user_id IN (
    SELECT
      u.user_id
    FROM
      users u
    LEFT JOIN
      orders o ON u.user_id = o.user_id
    WHERE
      o.order_id IS NULL AND u.registration_date < '2022-01-01'
  );

How it works: This SQL query demonstrates how to delete records from the `users` table based on conditions that involve another table (`orders`). The subquery identifies `user_id`s that have no associated orders (orphaned users) and registered before a specific date. The outer `DELETE` statement then removes all `users` whose `user_id` appears in the list generated by the subquery, effectively cleaning up inactive or orphaned user accounts.