Question

假设我在公司表中有两家公司1和公司2。每个公司有两个项目（项目1-1和项目1-2属于公司1.项目2-1和项目2-2属于公司2）。同样，每个项目都有两项费用（共8项费用）。我想列出所有公司，项目总预算和这些公司的总支出。 SQL查询（对于mysql）是什么样的？

公司表有两个字段（idfirm和name）。项目表有四个字段（idproject，name，budget和firm_idfirm作为外键）。最后，Expense表有三个字段（idexpense，amount和project_idproject作为项目表的idproject字段的外键引用。）

首先我尝试了这个查询

select firm.name as Firm, sum(project.budget) as Project, sum(expense.amount) as Expense
from firm, project, expense 
where firm.idfirm = project.firm_idfirm and project.idproject = expense.project_idproject
group by firm.name;

但其结果显示每家公司的费用总和是正确的，但每家公司的预算总和不是。似乎预算是重复的。有什么建议吗？

Answer 1

您需要分两步完成聚合。有几种表达方式，这就是我如何表达它......

SELECT
  firm.name as Firm, SUM(project.budget) as budget, SUM (expense.expense) AS expense
FROM
  firm
LEFT JOIN
  project
    ON firm.idfirm = project.firm_idfirm
LEFT JOIN
  (SELECT project_idproject, SUM(amount) AS expense FROM expense GROUP BY project_idproject) AS expense
    ON project.idproject = expense.project_idproject
GROUP BY
  firm.name;

Answer 2

至于为什么 budget总和是错误的，想象一下没有sum或group by的查询结果。每个相关的project.budget记录都会重复expense值，但sum不会考虑该值。它只是盲目地添加它们，使总和膨胀。

Answer 3

select  name, pbudget, peamount
from    firm
        inner join
        (select   firm_idfirm, sum(budget) as pbudget, sum(eamount) as peamount
        from      project
                  inner join
                  (select id, sum(amount) as eamount
                  from expense
                  group by project_idproject) e
        on e.project_idproject = project.id
        group by firm_idfirm) p
on firm.id = p.firm_idfirm

没有重复的Sql Sum

3 个答案: