Question

我有两列：总数和百分比。我已经使用Alias创建了一个新的总列，现在我想通过查找此列和Alias总列的总和得到一个百分比列。我试过的内容如下：

SELECT sum(CASE when quality_class =1  then
    trees_ha else 0 end)/get_total_forest_plots()  +
sum(CASE when quality_class =2  then
    trees_ha else 0 end)/get_total_forest_plots()  as total ,

(sum(CASE when quality_class =1  then
     trees_ha else 0 end)/get_total_forest_plots()  +   
sum(CASE when quality_class =3  then
    trees_ha else 0 end)/get_total_forest_plots())/sum(total) *100 as percentage from (SELECT nested query from my_table);

我使用了这个sum（total）方法，但是我得到的错误是ERROR：列“total”不存在。

Answer 1

是的，您不能在同一级别使用别名。您需要编写一个上层查询来使用别名考虑到代码的逻辑已经起作用，只需更正语法即可使用别名这是怎么回事

SELECT 
   sum(CASE when quality_class =1 then trees_ha else 0 end)/get_total_forest_plots() + sum(CASE when quality_class =3 then trees_ha else 0 end)/get_total_forest_plots())/sum(initial_data.total) *1
FROM
    (SELECT 
    sum(CASE when quality_class =1 then trees_ha else 0 end)/get_total_forest_plots() + sum(CASE when quality_class =2 then trees_ha else 0 end)/get_total_forest_plots() as total 
From
<Table name> 
) initial_data

Answer 2

选项1

SELECT 3 x, (SELECT 1+1) y, 3-(SELECT 1+1) z;

或

选项2

SELECT x, y, x-y z FROM
  ( SELECT 3 x, (SELECT 1+1) y) q

如何从MySQL中的Alias列计算总和？

2 个答案: