Oracle 21c

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CREATE TABLE citypop
    ("code" varchar2(2), "name" varchar2(7), "Year" int, "pop" int)
;
INSERT ALL 
    INTO citypop ("code", "name", "Year", "pop")
         VALUES ('OH', 'Cevland', 1998, 10000)
    INTO citypop ("code", "name", "Year", "pop")
         VALUES ('OH', 'Cevland', 2000, 1000)
    INTO citypop ("code", "name", "Year", "pop")
         VALUES ('OH', 'Dayton', 1998, 6000)
    INTO citypop ("code", "name", "Year", "pop")
         VALUES ('OH', 'Toledo', 1978, 8000)
    INTO citypop ("code", "name", "Year", "pop")
         VALUES ('WI', 'Madison', 1999, 2000)
    INTO citypop ("code", "name", "Year", "pop")
         VALUES ('WI', 'Madison', 2000, 20000)
    INTO citypop ("code", "name", "Year", "pop")
         VALUES ('WI', 'Racine', 2000, 5000)
SELECT * FROM dual
;
7 rows affected

WITH CITY_POP AS (
SELECT
 "code", "name", AVG("pop") avgpop
  ,ROW_NUMBER() OVER(PARTITION BY "code" ORDER BY  AVG("pop") DESC) rn
FROM citypop
GROUP BY "code", "name")
SELECT "name", avgpop FROM CITY_POP WHERE rn = 1


name
AVGPOP


Toledo
8000

Madison
11000