ALTER TABLE package ADD CONSTRAINT unique_package_id UNIQUE (package_id);

CREATE UNIQUE INDEX CONCURRENTLY package_tmp_id_idx ON answer (package_id);

prod_db=> ALTER TABLE package ADD CONSTRAINT
          unique_package_id UNIQUE (package) USING INDEX package_tmp_id_idx;

ERROR:  syntax error at or near "package_tmp_id_idx"
LINE 1: ...T unique_package_id UNIQUE (answer_id) USING INDEX package_tmp_id_idx...
                                                             ^