如何在不使用group by的情况下获得此sql查询的相同结果？

Question

I have a query which is as follows :

SELECT CO.CONTINENT, FLOOR(AVG(CI.POPULATION))
FROM CITY CI INNER JOIN COUNTRY CO
ON CI.COUNTRYCODE = CO.CODE
GROUP BY CO.CONTINENT;

Now, I would want to get the same result but without using Group by as I am looking for an alternative for learning purpose. I am sure this can be achieved using subquery but I am unable to.

I have tried following ways:

SELECT CO.CONTINENT, 
( SELECT FLOOR(AVG(CI2.POPULATION)) FROM CITY CI2 WHERE CI2.COUNTRYCODE = CO.CODE )
FROM CITY CI INNER JOIN COUNTRY CO
ON CI.COUNTRYCODE = CO.CODE;

or

SELECT CO.CONTINENT, FLOOR(AVG(CI.POPULATION)) OVER(PARTITION BY CI.COUNTRYCODE)
FROM CITY CI INNER JOIN COUNTRY CO
ON CI.COUNTRYCODE = CO.CODE;

Answer 1

Try this:

SELECT DISTINCT
    t.CONTINENT,
    (SELECT FLOOR(AVG(c2.POPULATION)) FROM COUNTRY c1 INNER JOIN CITY c2
     ON c1.CODE = c2.COUNTRYCODE WHERE c1.CONTINENT = t.CONTINENT) AS pop_avg
FROM COUNTRY t

By the way, DISTINCT sometimes is implemented under the hood using GROUP BY , but I don't know how to report each continent only once without doing this.

Answer 2

I don't really recommend this approach, but you can just do:

SELECT DISTINCT CO.CONTINENT, FLOOR(AVG(CI.POPULATION))
FROM CITY CI INNER JOIN
     COUNTRY CO
     ON CI.COUNTRYCODE = CO.CODE;