INSERT INTO schema.my_unique_values
     SELECT DISTINCT id, value
       FROM schema.a_huge_table
      WHERE NOT EXISTS (SELECT 1
                          FROM schema.my_unique_values)

INSERT INTO schema.my_unique_values
     SELECT DISTINCT id, value
       FROM schema.a_huge_table a
      WHERE NOT EXISTS
             (SELECT 1
                FROM schema.my_unique_values m
               WHERE m.id = a.id AND m.value = a.value)

INSERT INTO schema.my_unique_values
     SELECT DISTINCT id, value
       FROM schema.a_huge_table a
ON CONFLICT DO NOTHING ;

CREATE MATERIALIZED VIEW schema.my_unique_values AS
  SELECT DISTINCT id, value
  FROM schema.a_huge_table;

REFRESH MATERIALIZED VIEW schema.my_unique_values

REFRESH MATERIALIZED VIEW CONCURRENTLY schema.my_unique_values