SELECT id, max(status), col
FROM tbl
GROUP BY id

    -- ВМЕСТО:
SELECT DISTINCT ON (author_id) *
FROM b_p_t
ORDER BY author_id, ctime DESC

    -- НАДО:
CREATE OR REPLACE FUNCTION fast_distinct_on_test()
RETURNS SETOF b_p_t
LANGUAGE plpgsql AS $f$

DECLARE _b_p_t record;

BEGIN

--start from greatest author_id
SELECT * INTO _b_p_t FROM b_p_t ORDER BY author_id DESC, ctime DESC LIMIT 1;

LOOP

--finish if nothing found
EXIT WHEN _b_p_t IS NULL;

--return found value
RETURN NEXT _b_p_t;

--latest post from next author_id < current author_id
SELECT *

FROM b_p_t
INTO _b_p_t

WHERE author_id < _b_p_t.author_id.
ORDER BY author_id DESC, ctime DESC
LIMIT 1;

END LOOP;

END;
$f$;

SELECT DISTINCT ON (cid) cid, added
FROM client_owner co

WHERE added >= '2020-07-15 00:00:00'

ORDER BY cid, added
LIMIT 25

SELECT cid, min(added)
FROM client_owner co
GROUP BY cid
LIMIT 25

cid int -- один cid может иметь неск.записей
uid int
added tstz(0)