Question

I just found a bug in my Rails app which would lead to certain records not getting deleted with their associated objects. The bug has been fixed, but I now have several thousand records in my database with foreign key values pointing to records that don’t exist.

Is it possible to delete all records in a table where an integer foreign key references a record in another table that doesn’t exist in SQL? How?

Answer 1

delete from child_table where not exists 
   (select 1 from parent_table where parent_table.id=child_table.related_id)

the next step is of course to create a FOREIGN KEY constraint immediately (unless you’re on MySQL MyISAM in which case you’re out of luck on that).