Question

    (SELECT discount_percent
    FROM products
    WHERE discount_percent > AVG(discount_percent)

我不确定自己做错了什么

Answer 1

WHERE discount_percent >
    (SELECT discount_percent
    FROM products
    WHERE discount_percent > AVG(discount_percent)

应为：

WHERE discount_percent > (SELECT AVG(discount_percent) FROM products)

子查询后您缺少右括号。但是更大的问题是您不能在WHERE子句中使用聚合函数，因为聚合是在选择行之后完成的。另外，您需要使查询仅返回一个结果，以便可以将其与>进行比较。

Answer 2

WHERE discount_percent > AVG(discount_percent)
可能需要更改为
HAVING discount_percent > AVG(discount_percent)

HAVING子句用于过滤聚合函数，例如您正在调用的AVG。