MySQL AS 语句生成错误

Question

我正在阅读 Murach MySQL 书，但无法运行第 3 章中的练习之一，我不知道出了什么问题。 discount_amount 列导致:

ERROR 1054 (42S22): Unknown column 'list_price' in 'field list'

这就是我使用 AS 的原因。有人看到我的代码有什么问题吗？

SELECT product_name,
   list_price,
   discount_percent,
   list_price*discount_percent AS discount_amount,
   list_price-discount_amount AS discount_price,
   ROUND(discount_amount, 2),
   ROUND(discount_price, 2)
FROM products
ORDER BY discount_price DESC
LIMIT 5;

Answer 1

需要在ROUND中再次计算

SELECT product_name,
   list_price,
   discount_percent,
   list_price*discount_percent AS discount_amount,
   list_price-discount_amount AS discount_price,
   ROUND(list_price*discount_percent, 2),
   ROUND(list_price-discount_amount, 2)
FROM products
ORDER BY discount_price DESC
LIMIT 5;