Foreign keys and updates
Deleting the P row with p_id = 4 succeeds:
jao=# delete from p where p_id = 4;
DELETE 1
But deleting the P row with p_id = 1 fails:
jao=# delete from p where p_id = 1;
ERROR: update or delete on table "p" violates foreign key constraint "f_p_id_fkey" on table "f"
DETAIL: Key (p_id)=(1) is still referenced from table "f".
Updating that row's p_id also fails:
jao=# update P set p_id = 99 where p_id = 1;
ERROR: update or delete on table "p" violates foreign key constraint "f_p_id_fkey" on table "f"
DETAIL: Key (p_id)=(1) is still referenced from table "f".
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