https://www.postgresql.org/docs/15/tutorial-agg.html

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Page: https://www.postgresql.org/docs/15/tutorial-agg.html
Description:

city | max | count
---------+-----+-------
Hayward | 37 | 5
(1 row)
it's not right

SELECT city, max(temp_lo), count(*) FILTER (WHERE temp_lo < 30)
FROM weather
GROUP BY city
HAVING max(temp_lo) < 40;

city | max | count
---------+-----+-------
Hayward | 35 | 0

because
SELECT city, max(temp_lo), count(*) FILTER (WHERE temp_lo < 30)
FROM weather
WHERE city LIKE 'S%' -- (1)
GROUP BY city
HAVING max(temp_lo) < 40;
city | max | count
------+-----+-------
(0 rows)