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Selfhosted database won't create a relationship
Attribute with the requested key already exists. Attribute keys must be unique, try again with a different key. i want to create a relationship on my cards collection but it gives me this error i check the database with phpMyAdmin but i don't know what to change inside it.
TL;DR
Developer is unable to create a relationship in their self-hosted database due to an existing attribute key error. They are unsure how to resolve it when checking the database with phpMyAdmin. 
Do you already have a subCategories column?
