mysql - MySQL查询以获取基于动态数据的列

Question

如何获得 MySQL 返回的“利润”值。totalCost 和 totalSell 从数据库中获取。

select 
  sum(cost) as totalCost
  , sum(sell) as totalSell
  , (totalSell-totalCost) as profit 
from orders

Answer 1

您为什么不尝试直接计算利润而不是使用别名？

试试这个：

Select SUM(cost) AS totalCost
     , SUM(sell) AS totalSell
     , (SUM(sell) - SUM(cost)) AS profit
FROM orders

看到这个 SQLFiddle

Answer 2

您不能在select声明它们的查询部分中使用别名：

select sum(cost) as totalCost, 
       sum(sell) as totalSell, 
       sum(sell) - sum(cost) as profit
from orders

如果您想使用别名来执行此操作（出于某种原因），您可以在子查询中定义它们时这样做：

select *, totalCost - totalSell as profit
from ( select sum(cost) as totalCost, 
              sum(sell) as totalSell, 
       from orders ) t

Answer 3

不要对别名执行操作。您需要更改(totalSell-totalCost) 为 (sum(cost)-sum(sell))

 Select sum(cost) as totalCost  , sum(sell) as totalSell, (sum(cost)-sum(sell)) as profit
     from orders