Issue is still actual on Eureka ecs bugfest

Will address as a front-end story.

I don’t know good way for UI to understand if such assignment exist.

Hey - could the front-end just prevent statistical codes from being deleted if assigned to to at least one instance, holdings, item record? Thus address this issue?

The root cause of the issue is a trigger that checks if the statistical code is assigned to at least one instance, holdings, item record and raises an exception if yes. It’s needed to restrict deletion of the code in case it’s used.
The code of the trigger:

One possible solution here is to create intermediate tables for relations between the statistical code table and instance/holdings/item. If the logic relies on foreign keys instead of querying tables it will increase the performance of deletion but may a little affect performance of create/update/delete of instance/holdings/item.

Also, this solution will require a migration → populate already existing relations in newly created tables.