You mean on the from side? Yes, just drop the existing index and create a unique index. You can do that within the same transaction. Postgres already requires

You mean on the from side? Yes, just drop the existing index and create a unique index. You can do that within the same transaction. Postgres already requires the pointed to relation to have a unique index: => create table foo (id int); -- No unique index here. CREATE TABLE => create index foo_id on foo(id); CREATE INDEX => create table bar(foo int references foo(id)); ERROR: there is no unique constraint matching given keys for referenced table "foo"