Postgres: Can I associate index with FK constraint?
I am not 100% certain what you are asking.

Your query shows the association of foreign key constraints to indexes at the target.

There is no association between indexes on the source and foreign key constraints.

You can use this query to find all foreign keys which have no index at the source that supports fast updates and key modifications on the target table:

SELECT conrelid::regclass, conname
FROM pg_constraint AS c
WHERE c.contype = 'f'
  AND NOT EXISTS (SELECT 1 FROM pg_index AS i
                  WHERE i.indrelid = c.conrelid
                    AND (i.indkey::smallint[])[0:cardinality(c.conkey)-1] @&gt; c.conkey);


The strange condition will test if the first index columns are identical to the columns in the foreign key definition.