Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
How can I delete duplicate rows from a MySQL table when a foreign key relationship has already been setup up on those rows.
Can the duplicates be merged somehow and then foreign key updated with the new value?
If the foreign key is
ON DELETE CASCADE, then deleting the duplicate rows will also delete the dependent rows, e.g., if you have a tablecustomersand a tableorders, and a foreign key likeALTER TABLE orders ADD FOREIGN KEY customer_id REFERENCES customers (id) ON DELETE CASCADE, then deleting a customer will also delete that customer’s orders. Similarly, if the foreign key hasON DELETE SET NULL, then the orders will not be deleted, but theircustomer_idvalues will be set to NULL.If neither of these is the desired behaviour, craft a query that resolves the foreign key conflicts by altering the foreign key columns so that they reference the row you want to keep (i.e., update all orders to reference non-duplicate customers), then delete the offending rows.
Yet another alternative is to disable foreign key checks temporarily, but this will leave you with an inconsistent database, so I wouldn’t recommend this.