Question

我正在使用MySQL 5.1，我有两个表，项目和员工。员工（number_project）中有一个外键，它是项目的主键（code_project）。

---＆GT;确切地说：SQL Fiddle

我正在尝试使用此查询按部门获取项目的SUM：

SELECT emp.department_emp AS Department, SUM( pro.price ) AS total_department
FROM employee AS emp, projects AS pro
WHERE emp.number_project = pro.code_project
GROUP BY emp.department_emp

它返回：

DEPARTMENT  TOTAL_DEPARTMENTA
Accounting   2600
IT           4200

但它应该回归：

DEPARTMENT  TOTAL_DEPARTMENT
Accounting   1300
IT           4200

问题在于，当同一部门的员工在该项目中工作时，查询对同一项目进行多次汇总。

谢谢！

Answer 1

您可以使用“折叠”员工的子查询，从项目中任意选择一名员工的部门：

SELECT department,
       SUM(price) AS total_department
  FROM ( SELECT project.code_project AS project,
                project.price AS price,
                MIN(employee.department_emp) AS department
          FROM project
          JOIN employee
            ON project.code_project = employee.number_project
         GROUP
            BY project.code_project,
               project.price
       )
 GROUP
    BY department
;

（当然，如果一个项目有来自多个不同部门的员工，这会产生误导性结果，因为它会将项目的全部价格分配给其中一个部门。）

Answer 2

使用子查询创建唯一(department, project)组合的列表：

select  e.department_emp
,       sum(p.price)
from    (
        select  distinct department_emp
        ,       number_project
        from    Employee
        ) e
join    Projects p
on      p.code_project = e.number_project
group by
        e.department_emp

Working example at SQL Fiddle.

您的数据库可能会使用一些认真的工作。员工与项目的关系应该是多对多关系，而不是多对一关系。而名为“number”的字段不应该在另一个表中称为“代码”。

Answer 3

SELECT emp.department_emp AS Department，SUM（pro.price）AS total_department FROM（SELECT DISTINCT * 从员工AS emp，项目AS专业 WHERE emp.number_project = pro.code_project AS P GROUP BY emp.department_emp

MySQL - 使用SUM组合两个表

3 个答案: