Question

I’ve taken over the development of a web app that uses a mysql innodb database. The client has a lot of duplicate records in the db on accident. I’m building a merge tool to keep one record and push the other’s associated data to it.

So, for example because of a typo, I might have.

entity_id    entity_cat    common_name
--------------------------------------
abcdefg      customer      John Doe
hijklmn      customer      Jon Doe

I then have a bunch of tables that are linked to entity_id. I want to delete ‘hijklmn’, and have all of the associated data in other tables change their ‘customer_entity_id’ to ‘abcdef’.

The problem is, the relationships all have on delete cascade. Is there any way for me to merge these two records without losing any data?

Answer 1

With regards to your ON DELETE CASCADE issue, you can temporarily disable all foreign key constraints for the purpose of your query with the script template below:

ALTER TABLE `entities` NOCHECK CONSTRAINT ALL

-- commit query here

ALTER TABLE `entities` CHECK CONSTRAINT ALL