nicer examples for aggregate calls

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Page: https://www.postgresql.org/docs/14/tutorial-agg.html
Description:

currently, all of the examples are very simple, like

SELECT city, max(temp_lo)
    FROM weather
    WHERE city LIKE 'S%'            -- (1)
    GROUP BY city
    HAVING max(temp_lo) < 40;

this example would be more complex and would allow users to search for
clause "filter":

Finally, if we only care about cities whose names begin with “S” and we want
to calculate the number of observations in each city with temp_lo over 30,
we might do:

SELECT city, max(temp_lo), count(*) filter (temp_lo>30), 
    FROM weather
    WHERE city LIKE 'S%'            -- (1)
    GROUP BY city
    HAVING max(temp_lo) < 40;