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/*2. Create a foreign key on the core_email_queue_recipients table to delete Recipients records on cascade. The SQL query to create this foreign key is:*/
ALTER TABLE core_email_queue_recipients ADD FOREIGN KEY(message_id) REFERENCES core_email_queue(message_id) ON DELETE CASCADE;

DELETE FROM core_email_queue_recipients WHERE message_id NOT IN (SELECT message_id FROM core_email_queue);
DELETE FROM core_email_queue_recipients WHERE recipient_id < (SELECT recipient_id FROM (SELECT recipient_id FROM core_email_queue_recipients ORDER BY message_id ASC, recipient_id DESC LIMIT 1) AS r);