postgres create rule on insert do nothing if exists insert otherwise; RETURNING id

问题

In Postgres, is it possible to CREATE RULE which does nothing if some key exists but inserts otherwise. In either case it should return the id of the inserted/skipped row.

I need a rule, so please do not give alternates. I currently have the below rule that does nothing on conflicting inserts and I want to perform an insert with RETURNING id clause but I am getting the below error

ERROR:  cannot perform INSERT RETURNING on relation "fco_assets"
HINT:  You need an unconditional ON INSERT DO INSTEAD rule with a RETURNING clause.
********** Error **********

ERROR: cannot perform INSERT RETURNING on relation "fco_assets"
SQL state: 0A000
Hint: You need an unconditional ON INSERT DO INSTEAD rule with a RETURNING clause.

Below is my current rule

CREATE OR REPLACE RULE table_ignore AS
ON INSERT TO table
WHERE (EXISTS ( SELECT 1
       FROM table
      WHERE table.key::text = new.key::text)) DO INSTEAD NOTHING;

Thanks

来源：https://stackoverflow.com/questions/59846085/postgres-create-rule-on-insert-do-nothing-if-exists-insert-otherwise-returning