数据处理函数 / 使用聚合函数

SELECT
    Continent,
    AVG(Population)
FROM country
GROUP BY Continent


Continent AVG(Population)
Asia 72,647,562.74
Europe 15,871,186.95
North America 13,053,864.86
Africa 13,525,431.03
Oceania 1,085,755.35
Antarctica 0.00
South America 24,698,571.42

AVG() 返回某一列的平均值：它把该列各行的值求和，再除以行数。