如何使用计算值来计算另一个

Question

我正在使用mysql

我有一个查询，如下所示

Select 
  cost,
  (service_charge*(cost-Discount)) as service_charge,
  (service_tax*(cost-Discount+(service_charge*(cost-Discount)))) as service_tax
From VENDOR_ITEMS
WHERE vendor_items_id = 264

我的问题是我得到service_charge的值我可以在计算service_tax时使用它吗？

如果可能，请告诉我

Answer 1

您不能使用计算值来计算另一个，但您可以使用variables：

SELECT
  cost,
  @sc := (service_charge*(cost-Discount)) as service_charge,
  (service_tax*(cost-Discount+( @sc ))) as service_tax
FROM
  VENDOR_ITEMS
WHERE
  vendor_items_id = 264

Answer 2

你必须重复表达

Select cost ,
 (service_charge*(cost-Discount)) as service_charge ,
 (service_tax*(cost-Discount+((service_charge*(cost-Discount))*(cost-Discount)))) as service_tax 
From VENDOR_ITEMS WHERE vendor_items_id = 264