PostgreSQL AVG 函数
AVG
该 AVG() 函数返回数值列的平均值。
注意： NULL 值将被忽略。
保留两位小数
上面的示例返回了所有产品的平均价格，结果为 28.8663636363636364。
我们可以使用 ::NUMERIC 运算符将平均价格四舍五入到小数点后两位。
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