Add (change) foreign key constraint to an existing column in PostgreSQL

retrofit-foreign-key-constraint.sql

-- https://dba.stackexchange.com/questions/323851/add-foreign-key-constraint-to-existing-column-while-auto-generating-the-key-nam

alter table "Message"
-- drop the old constraint
drop constraint "Message_sender_fkey",
-- (re)add constraint but this time with cascading
add foreign key ("sender") references "Sender"("id") on delete cascade;